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/Vfx/ParticleVisibilityController.cs

@@ -3,13 +3,22 @@ using AcDream.Core.Vfx;
 
 namespace AcDream.App.Rendering.Vfx;
 
+internal interface IWorldSceneParticleVisibility
+{
+    void MarkVisibleCells(HashSet<uint> cellIds);
+
+    void CompleteFrame();
+
+    void AbortFrame();
+}
+
 /// <summary>
 /// Bridges the retained retail PView result into the next physics update's
 /// <c>CObjCell::IsInView</c> particle gate. The controller owns only immutable
 /// frame meaning: one completed viewer position plus the AC cells admitted by
 /// that completed view. It neither creates emitters nor performs rendering.
 /// </summary>
-public sealed class ParticleVisibilityController
+public sealed class ParticleVisibilityController : IWorldSceneParticleVisibility
 {
     public const float ExtendedRangeMultiplier = 2f;
 
@@ -70,6 +79,15 @@ public sealed class ParticleVisibilityController
         _hasCompletedWorldView = true;
     }
 
+    /// <summary>Discards the in-progress visibility product while preserving
+    /// the last completed view consumed by the update thread.</summary>
+    public void AbortFrame()
+    {
+        _buildingCellIds.Clear();
+        _frameUsesWorldView = false;
+        _frameOpen = false;
+    }
+
     public void Apply(ParticleSystem particles, float rangeMultiplier)
     {
         ArgumentNullException.ThrowIfNull(particles);