feat(ui): #15 migrate DebugOverlay to ImGui DebugPanel - 7 collapsing sections + diagnostics toggles

Replaces the 473-LOC custom-StbTrueTypeSharp DebugOverlay with an
ImGui-rendered DebugPanel using the I.1 widget extensions. Single
window with 7 CollapsingHeader sections; checkboxes are the primary
toggle surface; F-keys retained where they invoke real gameplay
actions, dropped where they only toggled panels.

Pieces:
- DebugVM (UI.Abstractions): read-through ViewModel with combat-event
  ring (cap 25), toast ring (cap 25), 4 diagnostic-flag bools
  (DumpMotion / DumpVitals / DumpOpcodes / DumpSky), 3 Action hooks
  (CycleTimeOfDay / CycleWeather / ToggleCollisionWires). Self-
  subscribes to CombatState.DamageTaken/DealtAccepted/Evaded* /
  Missed*/AttackDone/KillLanded - replaces the old BindCombat path.
- DebugPanel (UI.Abstractions): one ImGui window with sections
  Player Info, Performance, Compass (text-only - draw-list strip
  deferred to D.6), Help (BeginTable cheat-sheet), Combat events
  (TextColored by kind: Info=yellow, Warning=red, Error=deep red),
  Recent toasts, Diagnostics (Checkboxes for the 4 flags + Buttons
  for the 3 cycle/toggle actions).
- All 28 Snapshot data points covered: Fps, FrameMs, PlayerPos,
  HeadingDeg, CellId, OnGround, InPlayerMode, InFlyMode,
  VerticalVelocity, EntityCount, AnimatedCount, LandblocksVisible,
  LandblocksTotal, ShadowObjectCount, NearestObjDist, NearestObjLabel,
  Colliding, DebugWireframes, StreamingRadius, MouseSensitivity,
  ChaseDistance, RmbOrbit, HourName, DayFraction, Weather,
  ActiveLights, RegisteredLights, ParticleCount.
- GameWindow surgery (+252/-165): removed _debugOverlay field +
  snapshot builder block + Update/Draw calls; added _debugVm /
  _debugPanel construction in the if (DevToolsEnabled) block;
  added per-frame nearest-object scan cached for VM closures
  (zero cost when devtools off); helper methods CycleTimeOfDay /
  CycleWeather / ToggleCollisionWires / GetDebug* / GetActiveSensitivity.

F-key disposition:
- F1: repurposed - now toggles whole DebugPanel visibility.
- F2: kept - ToggleCollisionWires (also a Button in panel).
- F4 / F5 / F6: REMOVED - per-section toggles replaced by
  CollapsingHeader inside one window.
- F7: kept - CycleTimeOfDay (also Button).
- F8 / F9: kept - mouse-sensitivity adjust; toasts route to
  _debugVm.AddToast.
- F10: kept - CycleWeather (also Button).

DebugOverlay.cs DELETED (473 LOC). TextRenderer + BitmapFont kept
alive: UiHost references _debugFont and the future HUD-in-world
(D.6) will reuse both.

11 new DebugVM tests covering combat-event-ring subscription, toast
ring cap, diagnostic-flag toggles. UI.Abstractions.Tests: 96 -> 107.
Solution total: 989 green (243 Core.Net + 639 Core + 107 UI).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tests/AcDream.UI.Abstractions.Tests/Panels/Debug/DebugVMTests.cs

@@ -0,0 +1,288 @@
+using System.Numerics;
+using AcDream.Core.Combat;
+using AcDream.UI.Abstractions.Panels.Debug;
+
+namespace AcDream.UI.Abstractions.Tests.Panels.Debug;
+
+/// <summary>
+/// Tests for the Phase I.2 <see cref="DebugVM"/> — read-through ViewModel
+/// for the migrated debug panel. Verifies the combat-event subscription
+/// (replacing the old <c>DebugOverlay.BindCombat</c>), the toast ring
+/// cap, and that the diagnostic-flag bools round-trip without affecting
+/// the rest of the VM.
+/// </summary>
+public sealed class DebugVMTests
+{
+    /// <summary>
+    /// Build a minimal <see cref="DebugVM"/> with safe defaults for every
+    /// constructor source. Tests that don't care about a particular source
+    /// just leave it stubbed out.
+    /// </summary>
+    private static DebugVM NewVm(CombatState? combat = null)
+    {
+        combat ??= new CombatState();
+        return new DebugVM(
+            getPlayerPosition: () => Vector3.Zero,
+            getPlayerHeadingDeg: () => 0f,
+            getPlayerCellId: () => 0u,
+            getPlayerOnGround: () => true,
+            getInPlayerMode: () => false,
+            getInFlyMode: () => false,
+            getVerticalVelocity: () => 0f,
+            getEntityCount: () => 0,
+            getAnimatedCount: () => 0,
+            getLandblocksVisible: () => 0,
+            getLandblocksTotal: () => 0,
+            getShadowObjectCount: () => 0,
+            getNearestObjDist: () => float.PositiveInfinity,
+            getNearestObjLabel: () => "-",
+            getColliding: () => false,
+            getDebugWireframes: () => false,
+            getStreamingRadius: () => 2,
+            getMouseSensitivity: () => 1f,
+            getChaseDistance: () => 0f,
+            getRmbOrbit: () => false,
+            getHourName: () => "Dawnsong",
+            getDayFraction: () => 0.25f,
+            getWeather: () => "Clear",
+            getActiveLights: () => 0,
+            getRegisteredLights: () => 0,
+            getParticleCount: () => 0,
+            getFps: () => 60f,
+            getFrameMs: () => 16.7f,
+            combat: combat);
+    }
+
+    [Fact]
+    public void Constructor_ThrowsOnNullCombat()
+    {
+        Assert.Throws<ArgumentNullException>(() => new DebugVM(
+            getPlayerPosition: () => Vector3.Zero,
+            getPlayerHeadingDeg: () => 0f,
+            getPlayerCellId: () => 0u,
+            getPlayerOnGround: () => true,
+            getInPlayerMode: () => false,
+            getInFlyMode: () => false,
+            getVerticalVelocity: () => 0f,
+            getEntityCount: () => 0,
+            getAnimatedCount: () => 0,
+            getLandblocksVisible: () => 0,
+            getLandblocksTotal: () => 0,
+            getShadowObjectCount: () => 0,
+            getNearestObjDist: () => 0f,
+            getNearestObjLabel: () => "-",
+            getColliding: () => false,
+            getDebugWireframes: () => false,
+            getStreamingRadius: () => 0,
+            getMouseSensitivity: () => 1f,
+            getChaseDistance: () => 0f,
+            getRmbOrbit: () => false,
+            getHourName: () => "",
+            getDayFraction: () => 0f,
+            getWeather: () => "",
+            getActiveLights: () => 0,
+            getRegisteredLights: () => 0,
+            getParticleCount: () => 0,
+            getFps: () => 0f,
+            getFrameMs: () => 0f,
+            combat: null!));
+    }
+
+    [Fact]
+    public void ReadThrough_PullsLiveValuesPerAccess_NoCache()
+    {
+        // The VM does NOT cache; every property read goes through the
+        // backing Func<T>. Mutating an external box between two reads
+        // must surface immediately.
+        int counter = 0;
+        var vm = new DebugVM(
+            getPlayerPosition: () => Vector3.Zero,
+            getPlayerHeadingDeg: () => 0f,
+            getPlayerCellId: () => 0u,
+            getPlayerOnGround: () => true,
+            getInPlayerMode: () => false,
+            getInFlyMode: () => false,
+            getVerticalVelocity: () => 0f,
+            getEntityCount: () => ++counter,
+            getAnimatedCount: () => 0,
+            getLandblocksVisible: () => 0,
+            getLandblocksTotal: () => 0,
+            getShadowObjectCount: () => 0,
+            getNearestObjDist: () => 0f,
+            getNearestObjLabel: () => "-",
+            getColliding: () => false,
+            getDebugWireframes: () => false,
+            getStreamingRadius: () => 0,
+            getMouseSensitivity: () => 1f,
+            getChaseDistance: () => 0f,
+            getRmbOrbit: () => false,
+            getHourName: () => "",
+            getDayFraction: () => 0f,
+            getWeather: () => "",
+            getActiveLights: () => 0,
+            getRegisteredLights: () => 0,
+            getParticleCount: () => 0,
+            getFps: () => 0f,
+            getFrameMs: () => 0f,
+            combat: new CombatState());
+
+        Assert.Equal(1, vm.EntityCount);
+        Assert.Equal(2, vm.EntityCount);
+        Assert.Equal(3, vm.EntityCount);
+    }
+
+    [Fact]
+    public void DamageTaken_AppendsErrorEvent()
+    {
+        var combat = new CombatState();
+        var vm = NewVm(combat);
+
+        combat.OnVictimNotification(
+            attackerName: "Drudge", attackerGuid: 0x10u,
+            damageType: 0u, damage: 12u, hitQuadrant: 0u,
+            critical: 0u, attackType: 0u);
+
+        var events = vm.CombatEvents.ToList();
+        Assert.Single(events);
+        Assert.Equal(CombatEventKind.Error, events[0].Kind);
+        Assert.Contains("Drudge", events[0].Text);
+        Assert.Contains("12", events[0].Text);
+    }
+
+    [Fact]
+    public void DamageDealt_AppendsInfoEvent()
+    {
+        var combat = new CombatState();
+        var vm = NewVm(combat);
+
+        combat.OnAttackerNotification(
+            defenderName: "Drudge", damageType: 0u,
+            damage: 8u, damagePercent: 0.1f);
+
+        var events = vm.CombatEvents.ToList();
+        Assert.Single(events);
+        Assert.Equal(CombatEventKind.Info, events[0].Kind);
+        Assert.Contains("Drudge", events[0].Text);
+    }
+
+    [Fact]
+    public void EvadedIncoming_AppendsWarnEvent()
+    {
+        var combat = new CombatState();
+        var vm = NewVm(combat);
+
+        combat.OnEvasionDefenderNotification("Mosswart");
+
+        var events = vm.CombatEvents.ToList();
+        Assert.Single(events);
+        Assert.Equal(CombatEventKind.Warn, events[0].Kind);
+        Assert.Contains("Mosswart", events[0].Text);
+    }
+
+    [Fact]
+    public void CombatEventRing_CapsAtMax_DropsOldest()
+    {
+        var combat = new CombatState();
+        var vm = NewVm(combat);
+
+        // Pump well past the cap (25). The oldest entries must drop out.
+        for (int i = 0; i < 40; i++)
+        {
+            combat.OnAttackerNotification(
+                defenderName: $"Foe{i}", damageType: 0u,
+                damage: (uint)i, damagePercent: 0.1f);
+        }
+
+        var events = vm.CombatEvents.ToList();
+        Assert.Equal(DebugVM.MaxCombatEvents, events.Count);
+        // The newest entry must still be present.
+        Assert.Contains(events, e => e.Text.Contains("Foe39"));
+        // The oldest must have dropped.
+        Assert.DoesNotContain(events, e => e.Text.Contains("Foe0,") || e.Text == "Foe0");
+        Assert.DoesNotContain(events, e => e.Text.Contains("Foe5"));
+    }
+
+    [Fact]
+    public void Toast_RingCapsAtMaxRecent()
+    {
+        var vm = NewVm();
+
+        for (int i = 0; i < 30; i++)
+            vm.AddToast($"toast-{i}");
+
+        var toasts = vm.RecentToasts.ToList();
+        Assert.Equal(DebugVM.MaxRecentToasts, toasts.Count);
+        Assert.Contains(toasts, t => t.Text == "toast-29");
+        Assert.DoesNotContain(toasts, t => t.Text == "toast-0");
+    }
+
+    [Fact]
+    public void Toast_PreservesKind()
+    {
+        var vm = NewVm();
+        vm.AddToast("warning!", ToastKind.Warn);
+        vm.AddToast("error!", ToastKind.Error);
+
+        var toasts = vm.RecentToasts.ToList();
+        Assert.Equal(2, toasts.Count);
+        Assert.Contains(toasts, t => t.Text == "warning!" && t.Kind == ToastKind.Warn);
+        Assert.Contains(toasts, t => t.Text == "error!" && t.Kind == ToastKind.Error);
+    }
+
+    [Fact]
+    public void DiagnosticFlags_DefaultFalse_RoundTripIndependently()
+    {
+        var vm = NewVm();
+        Assert.False(vm.DumpMotion);
+        Assert.False(vm.DumpVitals);
+        Assert.False(vm.DumpOpcodes);
+        Assert.False(vm.DumpSky);
+
+        vm.DumpMotion = true;
+        Assert.True(vm.DumpMotion);
+        Assert.False(vm.DumpVitals);
+        Assert.False(vm.DumpOpcodes);
+        Assert.False(vm.DumpSky);
+
+        vm.DumpSky = true;
+        vm.DumpMotion = false;
+        Assert.False(vm.DumpMotion);
+        Assert.True(vm.DumpSky);
+    }
+
+    [Fact]
+    public void ToggleFlags_DoNotAffectCombatRing()
+    {
+        var combat = new CombatState();
+        var vm = NewVm(combat);
+
+        combat.OnAttackerNotification("X", 0u, 1u, 0.1f);
+        Assert.Single(vm.CombatEvents);
+
+        vm.DumpMotion = true;
+        vm.DumpVitals = true;
+        Assert.Single(vm.CombatEvents);
+    }
+
+    [Fact]
+    public void ActionHooks_InvokeSuppliedDelegates()
+    {
+        // The panel needs to invoke "cycle time", "cycle weather", "toggle
+        // collision wires" actions when the corresponding Button is
+        // clicked. The VM exposes these as Action; the panel calls them.
+        int timeHits = 0, weatherHits = 0, wireHits = 0;
+        var vm = NewVm();
+        vm.CycleTimeOfDay = () => timeHits++;
+        vm.CycleWeather = () => weatherHits++;
+        vm.ToggleCollisionWires = () => wireHits++;
+
+        vm.CycleTimeOfDay?.Invoke();
+        vm.CycleTimeOfDay?.Invoke();
+        vm.CycleWeather?.Invoke();
+        vm.ToggleCollisionWires?.Invoke();
+
+        Assert.Equal(2, timeHits);
+        Assert.Equal(1, weatherHits);
+        Assert.Equal(1, wireHits);
+    }
+}