#531 [API/Memory] signals.py connection leak - every signal operation leaks DB connection

File: api/blueprints/v1/signals.py:26-30. get_signal_service() creates DB connection with autocommit=True that is NEVER closed. Each call to send_signal or get_signals leaks a connection. IMPACT: Will exhaust database connections under load. FIX: Use context manager or make SignalService own connection lifecycle.