fix: restore application-level logging after uvicorn takes over root logger

[Kaiohz]

Changes

• Set root logger level to UVICORN_LOG_LEVEL in lifespan to override uvicorn's default WARNING level for app loggers
• Move alembic migrations from async lifespan to run_fastapi() sync block (same pattern as raganything)
• Add access_log=True to uvicorn.run()
• Add UVICORN_LOG_LEVEL config setting (default: info)
• Replace logger.error with logger.exception in except blocks
• Replace logger.debug with logger.info throughout codebase
• Add logger.info to route handlers for request tracing
• Change Dockerfile CMD from 'python -m src.main' to 'python src/main.py'
• Update .env.composable-agents with UVICORN_LOG_LEVEL

Tests

• Verified application-level INFO logs now appear in container logs
• Verified access logs (GET/POST) appear in container logs
• Verified startup logs (migrations, persistence init) appear correctly