Document duplicate deletion behavior in tool description

Adds important note that all archival memories with identical text
will be deleted when using flag_archival_memory_for_deletion.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[e-mail]>

tools/flag_memory_deletion.py

···
 
     The system will search for all archival memories with this exact text and delete them.
 
+    IMPORTANT: If multiple archival memories have identical text, ALL of them will be deleted.
+    Make sure the memory_text is unique enough to avoid unintended deletions.
+
     Args:
         reason: The reason why this memory should be deleted
         memory_text: The exact text content of the archival memory to delete