feat: Implement Alembic for database migrations, including configuration, baseline schema, and Docker integration.

[ronibhakta1]

Closes #167
This pull request introduces a comprehensive database migration system using Alembic, improves operational safety and developer experience with new Makefile commands, and updates the documentation and Docker setup to support these changes. The most significant updates are the addition of Alembic-based migrations (with an initial baseline), new Makefile targets for safe updates and migration management, and enhancements to developer tooling and documentation.

Database migrations and schema management:

• Added Alembic migration engine, including configuration files (alembic.ini, alembic/env.py), a migration script template (alembic/script.py.mako), and the initial baseline migration (alembic/versions/001_baseline_schema.py) for items and loans tables. This enables versioned, automated schema changes and safe upgrades. [1] [2] [3] [4]
• Updated the Docker API image to include Alembic and run migrations automatically on container startup, ensuring the database schema is always up-to-date. [1] [2]

Developer and operational tooling:

• Expanded the Makefile with new commands for safe updates (make update), database migrations (make migrate, make migrate-status, make migration, make migrate-rollback, make migrate-stamp, make squash-migrations), and a health check utility (make doctor). Added warnings to destructive commands and introduced make redeploy for safe code updates without data loss. [1] [2] [3]
• Added a doctor.sh script for comprehensive environment diagnostics, checking Docker, configuration, database, and disk space.

Documentation improvements:

• Updated README.md with sections on updating, database migrations, health checks, and clarified rebuild/update workflows. Added documentation for Alembic and new Makefile commands. [1] [2] [3] [4] [5]

Configuration and environment:

• Introduced a VERSION file to track the current release version, which is now copied into the Docker image. [1] [2]
• Changed environment variable from LENNY_RELOAD to LENNY_PRODUCTION for clearer dev/production mode switching, and updated related scripts. [1] [2]

Reliability and health:

• Added a healthcheck to the API service in compose.yaml to ensure the service is ready before dependent services start.

These changes lay the foundation for safe, automated upgrades, robust schema management, and improved developer experience.

[mekarpeles]

we probably don't need these plans checked in

[ronibhakta1]

Well, I was reusing the existing environment with different names to make things much clearer.