fix(settings): OP9 review residuals — restore SaveAudio live-apply pin, delete dead residues

Closes the OP9 combined review's findings (docs/research/2026-08-11-op9-review.md,
APPROVE-WITH-FIXES):

- MUST-FIX 1: SaveAudio -> ApplyAudio (OP6's Config-tab live-apply) lost
  its ONLY assertion when the retired SettingsVM save-order test was
  deleted. Restored directly on the now-public seam:
  SaveAudioPersistsThenPushesLiveApplyAudioWithTheSavedSnapshot pins
  persist-then-push order + the pushed snapshot;
  SaveAudioSkipsTheLivePushWhenPersistenceFails pins the failure ordering
  (a failed persist pushes nothing and commits nothing). Also closes
  SF-5: the OP6 effective-volume comment's 'target-audio assertion above'
  reference is real again and now names the restored test.
- SF-3: dead residues deleted — RuntimeSettingsController's private
  SaveCharacter (zero callers post-371197a3), ISettingsStorage.SaveCharacter
  + its JsonRuntimeSettingsStorage/FakeStorage implementations (the deleted
  private method was the only caller), and IngressShutdownRoots.Settings
  (zero readers since the view-model shutdown stage died). SettingsStore's
  PUBLIC SaveCharacter stays: it is the tested storage-API seam, and
  per-toon entries in existing settings.json files still load through the
  live LoadCharacter path.
- SF-2: code-structure.md's presentation-seam list no longer routes the
  settings preview through 'optional SettingsVM'.
- NIT 6: AP-196's retirement note now attributes LockUI (/lockui +
  PlayerDescription SetUiLocked convergence) and UseMouseTurning
  (Gameplay-tab macro + Config-tab row) to their real channels instead of
  folding all 13 members into the Character tab.

Full Release suite: 13,077 passed / 4 skipped / 0 failed (13,075 + the two
restored tests). One unnamed App-assembly failure appeared on the first
post-fix full run and did not reproduce on the isolated assembly rerun nor
a second full run — consistent with the known #250-class parallel-load
flake, recorded here for honesty rather than silently rerun.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/AcDream.App/Rendering/GameWindow.cs

@@ -1667,7 +1667,6 @@ public sealed class GameWindow :
             _retailUiLease,
             _uiHost,
             _runtime,
-            _runtimeSettings,
             _movementInput,
             _cameraInput,
             _windowCallbacks),

src/AcDream.App/Rendering/GameWindowLifetime.cs

@@ -72,7 +72,6 @@ internal sealed record IngressShutdownRoots(
     // Keeps failed physical UI bindings alive through native-window release.
     UiHost? RetainedUiHost,
     GameRuntime Runtime,
-    RuntimeSettingsController Settings,
     DispatcherMovementInputSource MovementInput,
     DispatcherCameraInputSource CameraInput,
     SilkWindowCallbackBinding? WindowCallbacks);

src/AcDream.App/Settings/RuntimeSettingsController.cs

@@ -28,8 +28,6 @@ internal interface IRuntimeSettingsStorage
 
     void SaveChat(ChatSettings chat);
 
-    void SaveCharacter(string toonKey, CharacterSettings character);
-
     void SaveCameraTurning(CameraTurningSettings cameraTurning);
 }
 
@@ -65,9 +63,6 @@ internal sealed class JsonRuntimeSettingsStorage : IRuntimeSettingsStorage
 
     public void SaveChat(ChatSettings chat) => _store.SaveChat(chat);
 
-    public void SaveCharacter(string toonKey, CharacterSettings character) =>
-        _store.SaveCharacter(toonKey, character);
-
     public void SaveCameraTurning(CameraTurningSettings cameraTurning) =>
         _store.SaveCameraTurning(cameraTurning);
 }
@@ -544,27 +539,6 @@ internal sealed class RuntimeSettingsController :
     /// <inheritdoc cref="ServerOptionsSeeded"/>
     public void NotifyServerOptionsSeeded() => ServerOptionsSeeded?.Invoke();
 
-    private void SaveCharacter(CharacterSettings character)
-    {
-        try
-        {
-            _storage.SaveCharacter(ActiveToonKey, character);
-            Character = character;
-            if (string.Equals(
-                    ActiveToonKey,
-                    DefaultToonKey,
-                    StringComparison.OrdinalIgnoreCase))
-            {
-                _defaultCharacter = character;
-            }
-            _log($"settings: character[{ActiveToonKey}] saved to {_storage.Location}");
-        }
-        catch (Exception ex)
-        {
-            _log($"settings: character save failed: {ex.Message}");
-        }
-    }
-
     private static QualitySettings ResolveQuality(QualityPreset preset) =>
         QualitySettings.WithEnvOverrides(QualitySettings.From(preset));
 }