feat(render #53): EntityClassificationCache.InvalidateEntity + tests

Idempotent removal of a cached entry by entity id. Tests #4 and #5 from
spec section 7.1 lock in the contract.

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

src/AcDream.App/Rendering/Wb/EntityClassificationCache.cs

@@ -62,4 +62,13 @@ internal sealed class EntityClassificationCache
             Batches = batches,
         };
     }
+
+    /// <summary>
+    /// Remove the cache entry for <paramref name="entityId"/>. No-op if the
+    /// id isn't cached.
+    /// </summary>
+    public void InvalidateEntity(uint entityId)
+    {
+        _entries.Remove(entityId);
+    }
 }