feat(chat): Campaign CH slice CH6c — window opacity + transparency setting

Retail's ChatInterface::SetOpacity (0x004F3120) fades the WHOLE composited
window surface with one alpha; UiRenderContext.ApplyAlpha already gated
DrawSprite/DrawRect/DrawFill (since 1da697ec, pre-CH6) but DrawStringDat and
DrawString still passed applyAlpha:false, so text stayed sharp over a
translucent window. Both now route through the same chokepoint.

RetailWindowOpacityController (new) subscribes to a new
RetailWindowManager.WindowRegistered event and drives every registered
window's live Opacity from keyboard-focus state, applied to EVERY window
(chat, floaties, vitals, toolbar, ...) rather than retail's ChatInterface-only
scope — register row AP-190, retiring the stale AP-40 "fixed 0.75, no focus
transition" row in the same commit.

Verified retail's shipped opacity defaults from the decomp (constructor
literals, no cdb needed): the base ChatInterface ctor sets
DefaultOpacity=0.5/ActiveOpacity=1.0, kept unmodified by the four floating
windows; gmMainChatUI's own ctor overrides the main window to 1.0/1.0
(always fully opaque). acdream ships one shared global default (0.5/1.0)
rather than replicating the per-class override — also AP-190. The linking
invariant (raising default above active drags active UP; lowering active
below default drags default DOWN — never a clamp) is ported verbatim as
ChatOpacityLink in AcDream.UI.Abstractions, shared by the live controller
and the new Settings -> Chat tab's two linked opacity sliders.

Persistence: ChatSettings.DefaultOpacity/ActiveOpacity round-trip through
SettingsStore; Save pushes both through IRuntimeSettingsTargets.SetChatOpacity
into the live controller, no restart required.

Rider (CH6a/b re-review): strengthened the grip-media regression guard past
a bare SpriteFile != 0 check — ChatLayoutConformanceTests now drives each
live grip through a real UiRenderContext/TextRenderer (backed by the
in-memory RecordingGpuDevice test double) and asserts the draw call chain
actually queued sprite geometry, via a new TextRenderer.DebugSpriteSegments
test-only accessor.

Full Release suite 12,459 passed / 4 skipped / 0 failed (baseline
12,420/4/0). No subagents, no client launches (session hard constraints);
pending the next connected user gate for visual confirmation.

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

src/AcDream.App/Settings/RuntimeSettingsController.cs

@@ -131,6 +131,15 @@ internal interface IRuntimeSettingsTargets
     /// <c>CharacterOption</c> id (e.g. <c>ListenToGeneralChat = 0x23</c>).
     /// </summary>
     void SetSingleCharacterOption(uint optionId, bool value);
+
+    /// <summary>
+    /// Campaign CH slice CH6c (2026-08-10): pushes the Chat tab's two linked
+    /// transparency sliders into the live <c>RetailWindowOpacityController</c> —
+    /// local-only (no server round-trip, unlike <see cref="SetSingleCharacterOption"/>),
+    /// applies with no restart, matches retail's own
+    /// <c>UpdateFromPlayerModule</c> call order (default before active).
+    /// </summary>
+    void SetChatOpacity(float defaultOpacity, float activeOpacity);
 }
 
 internal interface IRuntimeSettingsPreviewSource
@@ -541,6 +550,12 @@ internal sealed class RuntimeSettingsController :
         PublishHearOptionChange(
             previous.HearSocietyChat, chat.HearSocietyChat,
             (uint)CharacterOptionId.ListenToSocietyChat);
+
+        // CH6c: local-only live apply — unlike the Hear* options above, this never
+        // touches the wire (retail's 0x1000008C blob remains unparsed, per the
+        // window-shell research doc §4.4/§6.1). Always pushed (not diffed) so the
+        // linking invariant self-heals even if only one field nominally changed.
+        _runtimeTargets?.SetChatOpacity(chat.DefaultOpacity, chat.ActiveOpacity);
     }
 
     private void PublishHearOptionChange(bool previous, bool current, uint optionId)