feat(physics): CylSphere collision for trees, rocks, NPCs

Most scenery objects (trees, rocks) use CylSphere collision from
their Setup, not PhysicsBSP. Register these in ShadowObjectRegistry
with a Cylinder collision type. FindObjCollisions now handles both:
- BSP: full polygon collision via BSPQuery (buildings, stabs)
- Cylinder: radial + vertical cylinder-sphere test (trees, NPCs)

Diagnostics showed 170 CylSphere entities vs 278 BSP entities in
the Holtburg landblock alone — this roughly doubles collision coverage.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/AcDream.Core/Physics/ShadowObjectRegistry.cs

@@ -21,9 +21,10 @@ public sealed class ShadowObjectRegistry
     /// Register an entity into the cells it overlaps based on world position + radius.
     /// </summary>
     public void Register(uint entityId, uint gfxObjId, Vector3 worldPos, Quaternion rotation,
-                         float radius, float worldOffsetX, float worldOffsetY, uint landblockId)
+                         float radius, float worldOffsetX, float worldOffsetY, uint landblockId,
+                         ShadowCollisionType collisionType = ShadowCollisionType.BSP,
+                         float cylHeight = 0f)
     {
-        // Deregister first if already registered (handles position updates)
         Deregister(entityId);
 
         float localX = worldPos.X - worldOffsetX;
@@ -34,7 +35,7 @@ public sealed class ShadowObjectRegistry
         int minCy = Math.Max(0, (int)((localY - radius) / 24f));
         int maxCy = Math.Min(7, (int)((localY + radius) / 24f));
 
-        var entry = new ShadowEntry(entityId, gfxObjId, worldPos, rotation, radius);
+        var entry = new ShadowEntry(entityId, gfxObjId, worldPos, rotation, radius, collisionType, cylHeight);
         var cellIds = new List<uint>();
 
         uint lbPrefix = landblockId & 0xFFFF0000u;
@@ -146,9 +147,17 @@ public sealed class ShadowObjectRegistry
     public int TotalRegistered => _entityToCells.Count;
 }
 
+/// <summary>
+/// Collision type for a shadow entry. BSP uses full polygon collision.
+/// Cylinder uses a simple cylinder-sphere intersection test.
+/// </summary>
+public enum ShadowCollisionType : byte { BSP, Cylinder }
+
 public readonly record struct ShadowEntry(
     uint EntityId,
     uint GfxObjId,
     Vector3 Position,
     Quaternion Rotation,
-    float Radius);
+    float Radius,
+    ShadowCollisionType CollisionType = ShadowCollisionType.BSP,
+    float CylHeight = 0f);