Feature/opti

[Araon]

Coordinator

• Add thread-safety and concurrency: protect registered_workers with a lock and use a ThreadPoolExecutor for heartbeats and task submissions.
• Make heartbeats/submissions non-blocking and add request timeouts.
• Fix timestamp handling (use real datetime objects) and make DB session usage test-friendly (dynamic session factory + no with Session()).
• Improve testability: accept dict-style inputs for direct method calls and support SKIP_NETWORK_CALLS to disable network heartbeats in tests.

Scheduler

• Initialize Flask-SQLAlchemy/Migrate for better test overrides (defer/bind properly).
• Ensure GET /schedule/ response shape matches tests ( {"task": {...}}).

Dev / Docker / tests

• Update docker-compose.yml for correct build contexts and add a tests service to run pytest inside Compose.
• Add .env and top-level config.py (env-driven SQLALCHEMY_DATABASE_URI) to centralize config and allow in-memory DB for tests.
• Add coordinator_service.py shim for test imports and adjust tests to run reliably in containers.

Why: improves scalability (non-blocking coordinator), robustness (timeouts, locks), and testability (config overrides, in-container tests).