feat(physics): port full CTransition collision response from pseudocode

Replace simplified push-out with retail-faithful SlideSphere and
AdjustOffset from transition_pseudocode.md. Crease-projection between
collision normal and contact plane produces smooth wall-sliding.
Object collision uses proper rotation transform to object-local space.

SlideSphere (section 6): computes crease direction via cross product
of collision normal and contact plane normal, projects displacement
onto the crease, then applies the correction offset. Handles three
cases: crease exists, parallel same-direction, parallel opposing.

AdjustOffset (section 6): adds safety check to keep sphere above
contact plane by computing signed distance and pushing up along Z
when the sphere dips below.

FindObjCollisions: removes ad-hoc penetration push-out, now calls
SlideSphere after BSP hit detection for proper wall-slide behavior.

Also fixes: ShadowEntry gains Rotation field, tests updated to match
Register signature, unused variables removed from GameWindow.

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

src/AcDream.Core/Physics/ShadowObjectRegistry.cs

@@ -20,14 +20,12 @@ public sealed class ShadowObjectRegistry
     /// <summary>
     /// Register an entity into the cells it overlaps based on world position + radius.
     /// </summary>
-    public void Register(uint entityId, uint gfxObjId, Vector3 worldPos, float radius,
-                         float worldOffsetX, float worldOffsetY, uint landblockId)
+    public void Register(uint entityId, uint gfxObjId, Vector3 worldPos, Quaternion rotation,
+                         float radius, float worldOffsetX, float worldOffsetY, uint landblockId)
     {
         // Deregister first if already registered (handles position updates)
         Deregister(entityId);
 
-        // Compute which cells the entity's bounding sphere overlaps.
-        // Each cell is 24×24m within a 192m landblock.
         float localX = worldPos.X - worldOffsetX;
         float localY = worldPos.Y - worldOffsetY;
 
@@ -36,7 +34,7 @@ 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, radius);
+        var entry = new ShadowEntry(entityId, gfxObjId, worldPos, rotation, radius);
         var cellIds = new List<uint>();
 
         uint lbPrefix = landblockId & 0xFFFF0000u;
@@ -148,4 +146,9 @@ public sealed class ShadowObjectRegistry
     public int TotalRegistered => _entityToCells.Count;
 }
 
-public readonly record struct ShadowEntry(uint EntityId, uint GfxObjId, Vector3 Position, float Radius);
+public readonly record struct ShadowEntry(
+    uint EntityId,
+    uint GfxObjId,
+    Vector3 Position,
+    Quaternion Rotation,
+    float Radius);