diag(physics): probe whether Runtime's world frame and App's origin ever disagree

#283 step 1: prove or disprove reachability before restructuring ownership.

Runtime rebases its world frame the instant an accepted Position carries
TeleportAdvanced (RuntimePhysicsState.ObserveLocalWorldFrame). App's
LiveWorldOriginState rebases only once StreamingOriginRecenterCoordinator
.Advance observes IsOriginRecenterRetirementComplete - many frames later,
after the old window has fully retired. Between those two edges the owners can
disagree by the source-to-destination landblock delta, and anything converted
in the gap lands a multiple of 192 m from the geometry App is building. Same
failure family as the zero-offset bug 670f307c fixed, with a wrong origin
rather than a missing one.

Reasoning has already closed most of the window: the recenter detaches EVERY
resident landblock before adopting the new origin, so old-origin collision is
retired first. What remains is the narrow gap between Runtime's flip and App's
BeginOriginRecenter, while old-origin geometry is still resident. Whether that
is ever actually hit is an empirical question, and the campaign rule is that a
restructure needs evidence, not a hypothesis.

ACDREAM_PROBE_WORLD_FRAME=1 emits one [world-frame] line per DISAGREEMENT at
DatLiveEntityProjectionMaterializer's landblock->world conversion - the exact
App-side counterpart of Runtime's TryGetWorldFrameOffset, and the site that
already holds both owners, so no new dependency is introduced. Silence across
a portal run is the evidence that #283 is unreachable and can close as a
permanent invariant instead of an ownership move.

Measurement only: the probe never gates placement, and the flag lives in
PhysicsDiagnostics with the rest of the ACDREAM_PROBE_* family per the
diagnostic-owner rule rather than as a scattered env read.

Complete Release solution: 10,836 passed / 4 skipped / 0 failed.

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

src/AcDream.Runtime/Physics/RuntimePhysicsState.cs

@@ -546,6 +546,16 @@ public sealed class RuntimePhysicsState : IDisposable
         }
     }
 
+    /// <summary>
+    /// #283: the landblock Runtime currently treats as world-frame (0,0), or
+    /// 0 before the local-player Create publishes one. Read-only and
+    /// diagnostic — App compares it against its own
+    /// <c>LiveWorldOriginState</c> centre to detect the teleport-window
+    /// disagreement described on
+    /// <c>PhysicsDiagnostics.ProbeWorldFrameEnabled</c>.
+    /// </summary>
+    internal uint WorldFrameCenterLandblockId => _worldFrameCenterLandblockId;
+
     /// <summary>
     /// #284: records that this session's local-player Create was accepted,
     /// independently of whether it carried a usable landblock. The frame is