#367 MEDIUM: Connection leak in get_raw_db_connection docstring example

## Issue The docstring for get_raw_db_connection() in engine/db.py:515-547 shows improper usage: ```python conn = get_raw_db_connection() try: ... finally: conn.close() # BUG: destroys pooled connection! ``` Calling close() on a pooled connection destroys it instead of returning to pool. Should use db._pool.putconn(conn). ## Impact - Connection pool exhaustion under load - Workers can't acquire connections - System degradation ## Location engine/db.py:515-547 (docstring example) ## Fix Update docstring to show correct pattern OR use context manager exclusively