fix: sanitize topic parameter in tool_diary_write

agent_name and entry are validated via sanitize_name/sanitize_content,
but topic is stored raw into ChromaDB metadata. Apply the same
sanitize_name guard to reject null bytes, path traversal, and
oversized payloads.

mempalace/mcp_server.py

@@ -925,6 +925,7 @@ def tool_diary_write(agent_name: str, entry: str, topic: str = "general"):
     try:
         agent_name = sanitize_name(agent_name, "agent_name")
         entry = sanitize_content(entry)
+        topic = sanitize_name(topic, "topic")
     except ValueError as e:
         return {"success": False, "error": str(e)}