fix(rendering): publish scene deltas at update boundary

Move the ordinary shadow-scene drain out of the conditional spatial reconciler and into an explicit final update-frame commit phase. This publishes deltas after streaming, network, teleport, camera, and conditional reconciles even while world simulation is quiesced.

Release gate: 3,733 App tests / 3 skips; 8,217 complete-solution tests / 5 skips.

Co-Authored-By: OpenAI Codex <codex@openai.com>

src/AcDream.App/Update/RenderSceneUpdateCommitPhase.cs

@@ -0,0 +1,18 @@
+using AcDream.App.Rendering.Scene;
+
+namespace AcDream.App.Update;
+
+/// <summary>
+/// Publishes every render-projection delta at the final update/render
+/// boundary, after streaming, network, teleport, and camera-owned spatial
+/// mutations have completed.
+/// </summary>
+internal sealed class RenderSceneUpdateCommitPhase : IUpdateFrameCommitPhase
+{
+    private readonly RenderSceneShadowRuntime? _shadow;
+
+    public RenderSceneUpdateCommitPhase(RenderSceneShadowRuntime? shadow) =>
+        _shadow = shadow;
+
+    public void Commit() => _shadow?.DrainUpdateBoundary();
+}