fix(physics): route remote Positions on contact, not walkability (AP-140)

The two gates that decide whether an accepted remote Position is interpolated
or hard-snapped read `Airborne`, which is `!Body.OnWalkable` — WALKABILITY.
Retail reads CONTACT: InterpolationManager::adjust_offset @0x00555D30 gates its
entire body on `transient_state & 1` @0x00555D52, so a retail body in contact
with a non-walkable face still interpolates.

The two predicates disagree in exactly one state — in contact, not on walkable
ground — which 204d0ae0 turned from unreachable into ordinary. Before it, the
per-tick forge made every non-airborne remote walkable by construction, so the
disagreement could not occur.

Both gates now read `!Body.InContact`: ApplyRemoteContactRouting's flight
carve-out and OnPosition's player-remote arm.

`Airborne` is deliberately NOT re-derived from CONTACT. That would perturb all
five of its writers and contradict a pinned assertion in
RemoteTeleportPlacementTests.Apply_PendingGroundToSteepContact_ (InContact:
true, OnWalkable: false -> Assert.True(remote.Airborne)); a previous
implementer attempted it and correctly backed out rather than editing the
assertion. This narrower shape touches no existing test.

AP-140's register row is retired in this commit, as the row itself specified.

Honest scope: this is a faithfulness fix, not a visible one. ACE derives its
IsGrounded flag with the same floor_z test, so during a slide it almost
certainly reports not-grounded, the classifier returns NoPositionOperation, and
neither arm is taken. Expect no observable change against ACE.

Suite 11,027 passed / 4 skipped / 0 failed (baseline 11,023).

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

tests/AcDream.App.Tests/Physics/LiveEntityNetworkRemoteFarSnapIntegrationTests.cs

@@ -392,7 +392,13 @@ public sealed class LiveEntityNetworkRemoteFarSnapIntegrationTests
         fixture.AllowDestination();
         (RuntimeEntityRecord record, RemoteMotion remote, PhysicsBody body) =
             fixture.AddRemote(0x70004008u, Destination);
+        // AP-140 (retired 2026-08-04): "mid-arc" is retail's CONTACT_TS-clear
+        // (`InterpolationManager::adjust_offset` gates on `transient_state & 1`
+        // @0x00555D52), not the client `Airborne` walkability flag. Both are
+        // set here so the test states free flight in the terms the gate now
+        // reads AND the terms it used to.
         remote.Airborne = true;
+        remote.Body.TransientState = TransientStateFlags.Active;
         var target = new Vector3(60f, 10f, 7f);
 
         LiveEntityNetworkUpdateController.RemoteContactRouting routing =