fix: mark MD5 as non-security in miner drawer ID generation

Add usedforsecurity=False to hashlib.md5() calls in miner.py and
convo_miner.py to document that MD5 is used for deterministic ID
generation, not cryptographic security. Preserves stable drawer IDs
for backward compatibility with existing palaces.

Swapping to SHA-256 would change the ID formula and make existing
drawers unreachable on re-ingestion. PR #34 covers the MD5 sites
in knowledge_graph.py and mcp_server.py.

Verified: usedforsecurity kwarg is supported since Python 3.9
(project target per pyproject.toml line 10), confirmed via Context7
CPython docs.

mempalace/convo_miner.py

@@ -352,7 +352,7 @@ def mine_convos(
             chunk_room = chunk.get("memory_type", room) if extract_mode == "general" else room
             if extract_mode == "general":
                 room_counts[chunk_room] += 1
-            drawer_id = f"drawer_{wing}_{chunk_room}_{hashlib.md5((source_file + str(chunk['chunk_index'])).encode()).hexdigest()[:16]}"
+            drawer_id = f"drawer_{wing}_{chunk_room}_{hashlib.md5((source_file + str(chunk['chunk_index'])).encode(), usedforsecurity=False).hexdigest()[:16]}"
             try:
                 collection.add(
                     documents=[chunk["content"]],

mempalace/miner.py

@@ -202,7 +202,7 @@ def add_drawer(
     collection, wing: str, room: str, content: str, source_file: str, chunk_index: int, agent: str
 ):
     """Add one drawer to the palace."""
-    drawer_id = f"drawer_{wing}_{room}_{hashlib.md5((source_file + str(chunk_index)).encode()).hexdigest()[:16]}"
+    drawer_id = f"drawer_{wing}_{room}_{hashlib.md5((source_file + str(chunk_index)).encode(), usedforsecurity=False).hexdigest()[:16]}"
     try:
         collection.add(
             documents=[content],