feat: add automatic database initialization and recovery

- Add init_database() with alembic programmatic API and retry logic
- Add connection retry with exponential backoff (5 attempts)
- Improve error messages for connection/auth failures
- Add table existence check before seeding data
- Update startup event to run migrations before seeding
- Add wait-for-db.sh script for Docker containers
- Update Docker and docker-compose configurations

Quality gates: ruff ✓, mypy ✓, unit tests (8 passed)

docker-compose.yml

@@ -50,6 +50,8 @@ services:
     container_name: hq-api
     environment:
       DATABASE_URL: postgresql+asyncpg://${POSTGRES_USER:-headquarter}:${POSTGRES_PASSWORD:-headquarter}@postgres:5432/${POSTGRES_DB:-headquarter}
+      POSTGRES_HOST: postgres
+      POSTGRES_PORT: 5432
       REDIS_URL: redis://redis:6379/0
       JWT_SECRET: ${JWT_SECRET:-change-me-in-production}
       REPO_BASE_PATH: /data/repos