fix(world+streaming): trees-in-sky Z, O(1) anim, teleport near-ring + immediate unloads

Three apparatus-confirmed fixes from the world-load/FPS deep-dive (all live-verified).

1. trees-in-sky — scenery ground-Z now samples THIS landblock's OWN heightmap
   (TerrainSurface.SampleZFromHeightmap, lock-step with the physics terrain) instead
   of the global PhysicsEngine.SampleTerrainZ query. At build time the landblock isn't
   registered in physics yet, so that query could only return null OR a STALE
   neighbour's height — the previous location's terrain, still registered after a
   teleport recenter — planting scenery at the old altitude (+250..500m, confirmed via
   the [scenery-z-stale] probe). Own-heightmap is correct in every case; the query is
   removed. (GameWindow.BuildSceneryEntitiesForStreaming)

2. FPS per-hop — TickAnimations recovered each animated entity's server guid via an
   O(N) ReferenceEquals reverse scan over ALL _entitiesByServerGuid (which never
   evicts, so N climbs every teleport — the drops-with-each-hop sink). Replaced with
   ae.Entity.ServerGuid: O(1), exact-equivalent (the dict key IS entity.ServerGuid).
   (GameWindow.TickAnimations)

3. teleport arrival + bulk floating terrain — two streaming fixes:
   - Near-ring eager-apply: a teleport applies the destination's 3x3 surroundings
     (StreamingController.PriorityRadius) and holds the fade until they're resident
     (PhysicsEngine.IsNeighborhoodTerrainResident), so the player arrives in a loaded,
     collidable world instead of one landblock in the void.
   - Immediate unloads: DrainAndApply no longer throttles UNLOADS at the per-frame
     load budget — they're cheap (free GPU buffers, no upload). A teleport produced
     ~600 unloads draining at 4/frame, leaving the previous region resident for
     seconds (floating terrain) and accumulating across rapid hops (951 resident vs a
     625 window). Only GPU-upload LOADS are metered now. Cut out-of-window resident
     650 -> 63 and resident 951 -> 688 (live-verified via [resid-audit]).

Includes gated-off diagnostic probes (ACDREAM_PROBE_SCENERY_FRAME / _BLDG_REACH /
_STREAM_RESID) used to root-cause the above — zero-cost when unset, same pattern as
the committed tp-probe.

The pre-existing teleport-induced "terrain arcs in the sky" (present in the dd2eb8b
baseline too, with NONE of this work) are a SEPARATE bug — investigated next.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/AcDream.Core/Physics/PhysicsDataCache.cs

@@ -441,6 +441,12 @@ public sealed class PhysicsDataCache
     public void CacheBuilding(uint landcellId, IReadOnlyList<BldPortalInfo> portals, Matrix4x4 worldTransform,
                               uint modelId = 0u)
     {
+        // Lost-collision probe (REMOVABLE): record every cache attempt + whether it
+        // actually took (first-wins) so we can see if/when a landblock's buildings
+        // get cached after a teleport.
+        AcDream.Core.Physics.PhysicsDiagnostics.LogBuildingCache(
+            landcellId, cached: !_buildings.ContainsKey(landcellId));
+
         if (_buildings.ContainsKey(landcellId)) return;
         Matrix4x4.Invert(worldTransform, out var inverse);
         _buildings[landcellId] = new BuildingPhysics