This commit prepares the musiclink bot for production deployment on NixOS.
Changes:
- Refactored service layer to support Dependency Injection for API URLs.
- Added 'internal/bot/bot_integration_test.go' for mock-based integration testing.
- Added 'flake.nix' and 'flake.lock' for reproducible Nix builds.
- Added 'README.md', 'LICENSE', and '.gitignore'.
- Verified build and tests pass locally.
