fix(ui): gate — no void frames around the login wormhole; vitals icons centered

The login tunnel now covers from the first world-facing frame (the
sky-void backdrop can never present pre-tunnel) and holds through an
atomic tunnel-to-world swap at reveal completion — the void is
structurally unreachable on both edges, pinned by frame-sequence tests
across WorldSceneRenderer/WorldRevealCoordinator/LocalPlayerTeleport-
Controller/RuntimeWorldTransitState. Vitals detail icons draw at their
authored centered offsets in both stacked and side-by-side layouts.
Implemented and live-probed by the fix agent; finalized by the lead
after the agent parked post-verification (gates re-run green:
App 5512/3, Runtime 1747/0).

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

src/AcDream.App/Streaming/WorldRevealCoordinator.cs

@@ -244,6 +244,22 @@ internal sealed class WorldRevealCoordinator
         return acknowledged;
     }
 
+    /// <summary>
+    /// The login mirror of <see cref="ObserveMaterialized"/>: acknowledges
+    /// the login reveal's materialization/simulation-release edge (retail
+    /// resumes <c>CObjectMaint</c>/<c>CPhysics</c> when destination cells
+    /// stop blocking, <c>SmartBox::UseTime @ 0x00455483</c> — while the
+    /// tunnel is still in front). See
+    /// <c>RuntimeWorldTransitState.AcknowledgeLoginMaterialized</c>.
+    /// </summary>
+    public bool ObserveLoginMaterialized(long generation)
+    {
+        bool acknowledged =
+            _transit.AcknowledgeLoginMaterialized(generation);
+        RetryPendingHostWork();
+        return acknowledged;
+    }
+
     public void ObserveWorldViewportVisible()
     {
         RetryPendingHostWork();