#625 Architectural: Don't hold DB transaction during long task execution

**Current Behavior:** The inline_executor creates a SAVEPOINT before task execution (line 1560-1562) and releases it after storing results (line 1568). During task execution, the DB connection sits idle-in-transaction. **Problem:** Long-running tasks (>idle_in_transaction_session_timeout) cause PostgreSQL to kill the connection. Task completes but cannot store results. **Current Workaround:** Increased idle_in_transaction_session_timeout from 60s to 300s in docker-compose.yml. **Proper Architectural Fix:** 1. Execute tasks OUTSIDE of transaction scope 2. Only use transaction for checkpoint storage (quick operation) 3. Consider: task execution -> THEN open transaction -> store result -> commit **Affected Code:** - engine/interpreters/inline_executor.py:1559-1591 (execute_task_inline) - The SAVEPOINT pattern is for rollback on failure, but holds connection during execution **Risk if not fixed:** Tasks running >5 minutes will still hit the timeout. The workaround only extends the limit. **Alternative approaches:** 1. Periodic keepalive queries during task execution 2. Connection pool with health checks 3. Restructure to use optimistic concurrency instead of savepoints