feat(input): #23 Phase K.1c - retail-faithful keymap cutover + JSON persistence (muscle memory change)

Single bisectable commit where the user-visible keyboard layout
flips from acdream-current (W/S/A/D/Z/X) to canonical AC retail
(W/X/A/D/Z/C). The InputDispatcher abstraction landed in K.1a,
existing handlers cut over in K.1b, and now KeyBindings.RetailDefaults()
returns the byte-precise retail preset matching
docs/research/named-retail/retail-default.keymap.txt.

Movement (matches AC1 muscle memory):
- W/Up = MovementForward (run by default)
- X/Down = MovementBackup
- A/Left = MovementTurnLeft
- D/Right = MovementTurnRight
- Z = MovementStrafeLeft
- C = MovementStrafeRight
- Alt+A / Alt+Left = MovementStrafeLeft (Alt-flips-turn)
- Alt+D / Alt+Right = MovementStrafeRight
- LShift (Hold) = MovementWalkMode (default = run; held = walk)
- Q = MovementRunLock (autorun toggle)
- S = MovementStop (sets Ready stance / idle)
- Space = MovementJump (hold to charge)
- Y = Ready, G = Sitting, H = Crouch, B = Sleeping (postures)

Selection / targeting (18 bindings on punctuation cluster):
- F = SelectionPickUp, T = SelectionSplitStack, P = PreviousSelection
- Backspace/Minus/Equals = closest/prev/next CompassItem
- Backslash/[/] = closest/prev/next Item
- Apostrophe/L/Semicolon = closest/prev/next Monster
- Home = LastAttacker
- Slash/Comma/Period = closest/prev/next Player
- N/M = prev/next Fellow
- E = SelectionExamine
- R = UseSelected

UI:
- F1 = ToggleHelp; Shift+Ctrl+F1 = TogglePluginManager
- F3 = Allegiance, F4 = Fellowship, F5 = Spellbook, F6 = SpellComponents
- F8 = Attributes, F9 = Skills, F10 = World, F11 = Options (lights up
  the Settings panel in K.3), F12 = Inventory
- Alt+1/2/3/4 = ToggleFloatingChatWindow1/2/3/4
- Esc = EscapeKey, Shift+Esc = LOGOUT
- Numpad * = CaptureScreenshot

Hotbar / spellbook:
- 1-9 = UseQuickSlot_1..9 (hotbar) AND UseSpellSlot_1..9 (in MagicCombat
  scope - dormant until Phase L)
- Ctrl+1-9 = UseQuickSlot_1..9 (duplicate)
- Alt+5-9 = UseQuickSlot_14..18 (second bar)
- 0 / Ctrl+0 = CreateShortcut

Chat:
- Tab = ToggleChatEntry (focus chat input; subscriber stub-TODO in K.2)
- Return = EnterChatMode (send)

Combat (mode-dependent, dormant - Phase L lights up):
- Grave (`) = CombatToggleCombat
- Insert/PgUp/Delete/End/PgDn = melee power+attack-level OR missile
  accuracy+aim-level OR magic spell-tab nav + cast (resolved by
  scope at runtime once CombatState.CurrentMode lands).
- Ctrl+Insert/PgUp/Delete/PgDn = first/last spell tab + first/last spell

Emotes: U = Cry, I = Laugh, J = Wave, O = Cheer, K = PointState

Camera (numpad cluster + F2):
- F2 / Numpad/ = CameraActivateAlternateMode
- Numpad 4/6/8/2 = rotate left/right/up/down
- Numpad - / + = move toward / away
- Numpad 0 = ViewDefault, Numpad . = FirstPerson
- Numpad 5 = LookDown, Numpad Enter = MapMode

Scroll:
- Mouse wheel handled by dispatcher OnScroll path
- Ctrl+Up / Ctrl+Down = ScrollUp / ScrollDown

Acdream debug actions relocated from F-keys to Ctrl+F-keys to avoid
retail conflicts:
- Ctrl+F1 = AcdreamToggleDebugPanel
- Ctrl+F2 = AcdreamToggleCollisionWires
- Ctrl+F3 = AcdreamDumpNearby
- Ctrl+F7 = AcdreamCycleTimeOfDay
- Ctrl+F8 / Ctrl+F9 = AcdreamSensitivityDown / Up
- Ctrl+F10 = AcdreamCycleWeather
AcdreamToggleFlyMode + AcdreamTogglePlayerMode have NO keyboard
binding in retail-default. K.2 adds a DebugPanel button for fly
toggle and auto-enter player mode at login.

Total: 149 bindings.

JSON load/save:
- KeyBindings.LoadOrDefault(path): merge-over-defaults migration.
  Missing actions get default bindings; unknown actions in user
  file are skipped (preserves user customizations across action
  enum additions). Corrupt file warns + returns RetailDefaults
  without overwriting (don't blow away user's file silently).
- KeyBindings.SaveToFile(path): writes with schema version=1, alpha-
  sorted action names, alpha-sorted modifier keys for stable diffs.
- KeyBindings.DefaultPath() = %LOCALAPPDATA%/acdream/keybinds.json.

GameWindow startup:
- Replaces KeyBindings.AcdreamCurrentDefaults() call with
  KeyBindings.LoadOrDefault(KeyBindings.DefaultPath()) via a small
  LoadStartupKeyBindings() helper.
- Logs "keybinds: loaded N bindings from <path>" so launch.log
  shows the source of truth at session start.

Three deviations from plan:
1. LoadStartupKeyBindings() helper instead of inline initializer
   (field initializer can't call methods directly).
2. ToggleChatEntry subscriber is a no-op stub with TODO K.2 comment
   (ChatPanel doesn't expose FocusInput() yet; will add in K.2).
3. AcdreamRmbOrbitHold removed from RetailDefaults() to avoid
   double-binding RMB (SelectRight + RmbOrbitHold on the same chord
   would fire both subscribers). Chase-camera orbit will be replaced
   by MMB-hold mouse-look in K.2 - retail's CameraInstantMouseLook.

28 new tests:
- KeyBindingsRetailTests: 19 cases pinning every retail mapping
  (W/X movement, Z/C strafe, Tab=ToggleChatEntry, Shift+Esc=LOGOUT,
  Shift+Ctrl+F1=TogglePluginManager, MovementWalkMode=Hold,
  Acdream debug on Ctrl+F*, hotbar number-row variants, etc).
- KeyBindingsJsonTests: 9 cases (round-trip; missing file →
  defaults; corrupt → defaults + no-overwrite; merge-over-defaults;
  legacy version=0 parsing; Hold-activation preservation; unknown-
  action skip; DefaultPath shape).

Solution total: 1162 green (243 Core.Net + 254 UI + 665 Core),
0 warnings.

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

src/AcDream.App/Rendering/GameWindow.cs

@@ -412,8 +412,20 @@ public sealed class GameWindow : IDisposable
     private AcDream.App.Input.SilkKeyboardSource? _kbSource;
     private AcDream.App.Input.SilkMouseSource? _mouseSource;
     private AcDream.UI.Abstractions.Input.InputDispatcher? _inputDispatcher;
-    private readonly AcDream.UI.Abstractions.Input.KeyBindings _keyBindings =
-        AcDream.UI.Abstractions.Input.KeyBindings.RetailDefaults();
+    // K.1c: load user-customized bindings from %LOCALAPPDATA%\acdream\keybinds.json,
+    // falling back to the retail-faithful defaults if the file is missing
+    // or corrupt. This is THE single source of truth for the keymap at
+    // startup — no other call to RetailDefaults() / AcdreamCurrentDefaults()
+    // should land in the GameWindow construction path.
+    private readonly AcDream.UI.Abstractions.Input.KeyBindings _keyBindings = LoadStartupKeyBindings();
+
+    private static AcDream.UI.Abstractions.Input.KeyBindings LoadStartupKeyBindings()
+    {
+        var path = AcDream.UI.Abstractions.Input.KeyBindings.DefaultPath();
+        var bindings = AcDream.UI.Abstractions.Input.KeyBindings.LoadOrDefault(path);
+        Console.WriteLine($"keybinds: loaded {bindings.All.Count} bindings from {path}");
+        return bindings;
+    }
 
     // Phase 4.7: optional live connection to an ACE server. Enabled only when
     // ACDREAM_LIVE=1 is in the environment — fully backward compatible with
@@ -5018,6 +5030,15 @@ public sealed class GameWindow : IDisposable
                 TogglePlayerMode();
                 break;
 
+            case AcDream.UI.Abstractions.Input.InputAction.ToggleChatEntry:
+                // K.1c: Tab in retail focuses the chat input. Phase K.2
+                // wires this to ChatPanel.FocusInput() once the panel grows
+                // an explicit focus method; the current ImGui-backed chat
+                // panel takes focus on click. Press is logged via the
+                // [input] diagnostic above so the cutover is observable.
+                // TODO K.2: call _chatPanel.FocusInput() once available.
+                break;
+
             case AcDream.UI.Abstractions.Input.InputAction.EscapeKey:
                 if (_cameraController?.IsFlyMode == true)
                     _cameraController.ToggleFly();  // exit fly, release cursor