refactor(ui): own retained controller lifetimes

src/AcDream.App/UI/README.md

@@ -38,6 +38,9 @@ synthesis + six deep-dive docs under
   geometry events, lock propagation, and controller teardown.
 - `IRetainedPanelController.cs` — disposable lifecycle contract for
   panel-specific show/hide and descendant-focus behavior.
+- `RetainedPanelControllerGroup.cs` — one typed lifecycle owner for windows
+  whose imported subtree is bound by multiple focused controllers; teardown is
+  idempotent and runs in reverse construction order.
 - `RetailWindowLayoutPersistence.cs` / `IRetainedWindowStateController.cs` —
   per-character/per-resolution bounds, visibility, collapse/maximize, legacy
   migration, and safe resolution-clamped restore.
@@ -45,7 +48,8 @@ synthesis + six deep-dive docs under
   contract for imported-chrome and shared-wrapper windows.
 - `UiHost.cs` — one-shot wrapper: owns the `UiRoot`, a `TextRenderer`,
   and a default `BitmapFont`. Provides `WireMouse` / `WireKeyboard`
-  helpers for Silk.NET plumbing.
+  helpers for Silk.NET plumbing and removes those device subscriptions before
+  disposing the window manager/controllers and renderer.
 
 ## Integration pattern