fix(physics): #42 skip self in FindObjCollisions — airborne XY drift

Root cause confirmed via two-run diagnostic and the named-retail decomp:
the airborne sweep was colliding with the moving entity's OWN ShadowEntry
because FindObjCollisions had no self-skip filter. Live entities (local
player, remotes) register a Cylinder in ShadowObjectRegistry on spawn
(GameWindow.cs:2545) and UpdatePosition tracks its world position each
tick, so the moving sphere's own cylinder is always at the body's
position. Without a gate, CylinderCollision sees the sphere overlapping
its own cylinder volume and slides the sphere ~1m horizontally on every
frame the path produces non-zero motion.

Why grounded mostly hides it and airborne exposes it:
- Stationary grounded → numSteps=0, TransitionalInsert never runs.
- Walking grounded → push fires but motion escapes the cyl radius and
  the deflection blends into normal motion.
- Stationary airborne (jump) → pure +Z motion; the cyl push is the
  only horizontal contribution and manifests as a clean ~1m drift.

Run-2 evidence (launch-42-r2.log) — 152 [SWEEP-OBJ] events, every one
with type=Cylinder, gfxObj=0x02000001 (humanoid setup), R=0.679,
H=1.835, at obj.Position EXACTLY matching the body's pre.Position. Run
1 had already ruled out H1 (cpN=(0,0,1) flat, no slope projection).

Retail does the same skip — CObjCell::find_obj_collisions at
named-retail acclient_2013_pseudo_c.txt:308931:

    if ((physobj->parent == 0 && physobj != arg2->object_info.object))

`arg2->object_info.object` is the OBJECTINFO::object self-pointer set
by OBJECTINFO::init at acclient_2013_pseudo_c.txt:274435. Our port
mirrors this with an EntityId-based filter:

  - ObjectInfo gains a SelfEntityId field (default 0 = no filter).
  - ResolveWithTransition gains an optional `uint movingEntityId = 0`
    parameter that sets it.
  - FindObjCollisions skips entries whose EntityId matches
    SelfEntityId when the id is non-zero.
  - PlayerMovementController gains a LocalEntityId property; GameWindow
    refreshes it per-tick from `_entitiesByServerGuid[_playerServerGuid]`.
  - GameWindow's airborne-remote ResolveWithTransition call site passes
    `movingEntityId: kv.Key` (kv.Key is the local entity id keying
    `_animatedEntities`, same id used at the spawn-time
    ShadowObjects.Register).

Default 0 keeps tests and one-shot callers (no registered ShadowEntry)
working unchanged.

Lock-the-fix unit test:
`PhysicsEngineTests.ResolveWithTransition_SelfShadowEntry_NotPushedWhenIdMatches`
registers a humanoid Cylinder at the body's exact position (matching
GameWindow's spawn pattern), then asserts that:
  - movingEntityId=0 (control)        → unfiltered XY drift > 0.5m
  - movingEntityId=registered id (fix) → XY drift ≈ 0

Diagnostic wiring (a36369d + this commit's [SWEEP-OBJ] addition) stays
in tree, env-var gated (ACDREAM_AIRBORNE_DIAG=1) so it produces no
output in normal use but lets us verify the fix on the live client and
debug future regressions.

Build: green. Tests: 355 pass, 6 fail (all pre-existing per the handoff
prompt — verified by stashing this change; the BSPStepUp C3 failure is
on the prior commit too).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/AcDream.App/Rendering/GameWindow.cs

@@ -5264,6 +5264,18 @@ public sealed class GameWindow : IDisposable
                 MouseDeltaX: 0f,
                 Jump:        _inputDispatcher.IsActionHeld(AcDream.UI.Abstractions.Input.InputAction.MovementJump));
 
+            // Fix #42 (2026-05-05): keep PlayerMovementController's
+            // LocalEntityId in sync with the live local player entity so
+            // FindObjCollisions skips its own ShadowEntry. Re-fetched per
+            // tick so re-spawns / character switches don't leave a stale
+            // id on the controller. Pre-spawn or between-character it
+            // stays 0 (no filter), which is harmless because there's no
+            // ShadowEntry registered yet.
+            _playerController.LocalEntityId =
+                _entitiesByServerGuid.TryGetValue(_playerServerGuid, out var localEnt)
+                    ? localEnt.Id
+                    : 0u;
+
             var result = _playerController.Update((float)dt, input);
 
             // Update the player entity's position + rotation so it renders at
@@ -6487,7 +6499,16 @@ public sealed class GameWindow : IDisposable
                             // Retail default physics state includes EdgeSlide.
                             // Remote dead-reckoning should exercise the same
                             // edge/cliff branch as local movement.
-                            moverFlags: AcDream.Core.Physics.ObjectInfoState.EdgeSlide);
+                            moverFlags: AcDream.Core.Physics.ObjectInfoState.EdgeSlide,
+                            // Fix #42 (2026-05-05): skip the moving remote's
+                            // own ShadowEntry. _animatedEntities is keyed by
+                            // entity.Id so kv.Key matches the EntityId the
+                            // ShadowObjectRegistry has for this remote.
+                            // Without this, the airborne sweep collides with
+                            // the remote's own cylinder and produces ~1m of
+                            // horizontal drift on the first jump frame
+                            // (validated by [SWEEP-OBJ] traces).
+                            movingEntityId: kv.Key);
 
                         rm.Body.Position = resolveResult.Position;
                         if (resolveResult.CellId != 0)