fix: resolve hooks_cli.py merge conflict + add mine_global_lock tests

- Resolve UU conflict in hooks_cli.py: take develop/HEAD approach
  (mine synchronously via _mine_sync, then pass through unconditionally).
  _mine_sync already catches subprocess.TimeoutExpired — fixes Copilot #1.
- Add tests/test_palace_locks.py: 4 tests covering mine_global_lock
  non-blocking semantics (acquire, second-acquire raises MineAlreadyRunning,
  reusable after release, release on exception) — fixes Copilot #4.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

mempalace/backends/chroma.py

@@ -566,7 +566,9 @@ class ChromaBackend(BaseBackend):
 
         if create:
             collection = client.get_or_create_collection(
-                collection_name, metadata={"hnsw:space": hnsw_space}, **ef_kwargs
+                collection_name,
+                metadata={"hnsw:space": hnsw_space, "hnsw:num_threads": 1},
+                **ef_kwargs,
             )
         else:
             collection = client.get_collection(collection_name, **ef_kwargs)
@@ -613,7 +615,9 @@ class ChromaBackend(BaseBackend):
         ef = self._resolve_embedding_function()
         ef_kwargs = {"embedding_function": ef} if ef is not None else {}
         collection = self._client(palace_path).create_collection(
-            collection_name, metadata={"hnsw:space": hnsw_space}, **ef_kwargs
+            collection_name,
+            metadata={"hnsw:space": hnsw_space, "hnsw:num_threads": 1},
+            **ef_kwargs,
         )
         return ChromaCollection(collection)