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>

docs/architecture/code-structure.md

@@ -208,8 +208,12 @@ documentation, not an exhaustive allowlist):
 - `DevToolsFramePresenter -> DevToolsPanelSet -> panel/ViewModel bindings` for
   the optional developer UI.
 - `WorldRenderFrameBuilder -> RuntimeWorldFrameSettingsPreview ->
-  IRuntimeSettingsPreviewSource -> RuntimeSettingsController -> optional
-  SettingsVM` for the live settings draft preview applied before world drawing.
+  IRuntimeSettingsPreviewSource -> RuntimeSettingsController` for the settings
+  snapshot read before world drawing. (The `SettingsVM` draft-preview tail of
+  this seam was retired at Campaign OP slice OP9 — the preview source now
+  mirrors the committed Display/Audio snapshot directly; the retail Options
+  panel applies its edits live through `SaveDisplay`/`SaveAudio` instead of a
+  draft layer.)
 - `LocalPlayerPortalViewport -> LocalPlayerTeleportController ->
   GameplayInputFrameController -> InputDispatcher.Fired -> GameWindow` for the
   canonical portal/input lifetime and the host's input-action subscription.