refactor(render): extract world scene frame owner

Move fallback and PView world drawing, shared alpha, particles, visibility, selection, and diagnostics behind focused frame owners. Make exceptional frames failure-atomic by restoring the shared GL baseline and preserving primary alpha failures through cleanup.

Co-authored-by: Codex <codex@openai.com>

src/AcDream.App/Rendering/WorldRenderFrameBuilder.cs

@@ -61,6 +61,18 @@ internal readonly record struct WorldRenderFrame(
     public LoadedCell? ClipRoot => Roots.ViewerRoot ?? Buildings.OutdoorNode;
 }
 
+internal interface IWorldRenderFrameBuilder
+{
+    WorldRenderFrame Build(
+        in RenderFrameFoundation foundation,
+        bool waitingForLogin,
+        DayGroupData? activeDayGroup);
+
+    void ObserveDrawableCells(IReadOnlySet<uint> drawableCells);
+
+    void ClearDrawableCells();
+}
+
 internal interface IWorldFrameCameraSource
 {
     WorldCameraFrame Resolve();
@@ -113,7 +125,7 @@ internal interface IWorldFrameBuildingSource
 /// Orders typed world-frame fact sources without owning their borrowed render
 /// resources. It makes no draw decision and retains no result from a prior call.
 /// </summary>
-internal sealed class WorldRenderFrameBuilder
+internal sealed class WorldRenderFrameBuilder : IWorldRenderFrameBuilder
 {
     private readonly IWorldFrameCameraSource _camera;
     private readonly IWorldFrameVisibilityPreparation _visibility;