feat(ui): Gameplay tab — 14 retail CharacterOption-derived toggles

Phase L.0 (cont.) — third tab on the Settings shell, in the Easy-wins
build order. Subset of retail's CharacterOption + CharacterOptions2
bitfield flags ported as bools (see acclient.h:3404+ enum). Local-
only this phase per the brainstorm — server sync deferred to a
later phase that will marshal the draft into the retail
CharacterOption packet.

GameplaySettings record exposes 14 named flags grouped by usage:

 · Combat: AutoTarget, AutoRepeatAttack, ToggleRun, AdvancedCombatUI,
   VividTargetingIndicator
 · Display: ShowTooltips, SideBySideVitals, CoordinatesOnRadar,
   SpellDuration, ShowHelm, ShowCloak
 · Interface: AllowGive, LockUI, UseMouseTurning

Retail names + bit values are documented in field-level comments so
the future server-sync phase has a 1:1 mapping. Defaults are
typical-user starting points (NOT bit-exact to retail's
0x50C4A54A / 0x948700 masks); class-level remarks call out that
defaults will be re-anchored to retail values once the wire-format
is the load-bearing source.

SettingsStore grows LoadGameplay / SaveGameplay using the existing
SaveSection generic helper (added in the audio commit). All three
non-keybind sections (display, audio, gameplay) now coexist in
settings.json with non-destructive cross-section saves — verified
by a new "all three sections coexist" round-trip test.

SettingsVM grows the parallel gameplay state machine
(gameplayPersisted / gameplayDraft / SetGameplay / onSaveGameplay).
HasUnsavedChanges, Save, Cancel, ResetAllToDefaults all cover
gameplay too. Constructor signature adds two more params; existing
call sites (App startup + tests) updated.

SettingsPanel.RenderGameplayTab replaces the L.0-shell placeholder —
14 Checkbox calls grouped under three Text+Separator headers, plus
a footer note explaining the local-only-this-phase scope. The
"Coming soon" placeholder test was retargeted from "Gameplay" to
"Chat" since Gameplay is no longer a placeholder.

GameWindow construction site loads gameplay on startup + writes via
the SettingsStore on Save. Server-sync packet wiring is left as a
TODO comment in the onSaveGameplay callback (next phase, after the
protocol round-trip is in place).

14 new tests:
 · GameplaySettings record (3) — defaults pinned, value equality,
   with-expressions
 · SettingsStore gameplay (4) — missing-file → defaults, round-trip,
   partial-file fallback, all-three-sections coexist
 · SettingsVM gameplay (5) — initial draft, SetGameplay marks dirty,
   Save invokes callback, Cancel reverts, ResetAllToDefaults covers
 · SettingsPanel gameplay tab (2) — 8 spot-checked Checkboxes render
   only when active

dotnet build green (0 warnings); dotnet test 1,276 / 1,276 green
(243 Core.Net + 360 UI.Abstractions + 673 Core).

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

src/AcDream.App/Rendering/GameWindow.cs

@@ -906,8 +906,9 @@ public sealed class GameWindow : IDisposable
                     // which keeps its own load/save path.
                     var settingsStore = new AcDream.UI.Abstractions.Panels.Settings.SettingsStore(
                         AcDream.UI.Abstractions.Panels.Settings.SettingsStore.DefaultPath());
-                    var persistedDisplay = settingsStore.LoadDisplay();
-                    var persistedAudio   = settingsStore.LoadAudio();
+                    var persistedDisplay  = settingsStore.LoadDisplay();
+                    var persistedAudio    = settingsStore.LoadAudio();
+                    var persistedGameplay = settingsStore.LoadGameplay();
 
                     // Apply persisted audio to the engine BEFORE the panel
                     // host starts pushing per-frame so the first frame uses
@@ -968,6 +969,24 @@ public sealed class GameWindow : IDisposable
                             {
                                 Console.WriteLine($"settings: audio save failed: {ex.Message}");
                             }
+                        },
+                        persistedGameplay: persistedGameplay,
+                        onSaveGameplay: gameplay =>
+                        {
+                            try
+                            {
+                                settingsStore.SaveGameplay(gameplay);
+                                Console.WriteLine(
+                                    "settings: gameplay saved to "
+                                    + AcDream.UI.Abstractions.Panels.Settings.SettingsStore.DefaultPath());
+                                // Local-only this phase. Server-sync packet
+                                // (CharacterOption bitmask) goes in here when
+                                // the protocol round-trip is in place.
+                            }
+                            catch (Exception ex)
+                            {
+                                Console.WriteLine($"settings: gameplay save failed: {ex.Message}");
+                            }
                         });
                     _settingsPanel = new AcDream.UI.Abstractions.Panels.Settings.SettingsPanel(_settingsVm);
                     _panelHost.Register(_settingsPanel);