This PR implements full support for Debian 13 (Trixie) and Alpine Linux server validation, prerequisites installation, and Docker setup.

Changes

Debian 13 (Trixie) Support

• Dynamic Docker repository fallback: Checks if Docker’s APT repository has the VERSION_CODENAME distribution. If not available (e.g., trixie), automatically falls back to bookworm
• This is future-proof and will work automatically when Docker eventually adds trixie support

Alpine Linux Support

• Complete prerequisites installation using apk package manager
• Docker installation using Alpine’s native packages (docker, docker-cli-compose)
• OpenRC service management (rc-update/service) instead of systemd

Testing

• Added unit tests covering all new functionality
• Tests verify command generation and OS-specific handling

Why This Approach is Better

1. Dynamic repo checking vs hardcoded codename mapping - automatically adapts when Docker adds trixie support
2. No changes to SUPPORTED_OS needed - Debian 13 already matches via ID=debian
3. Complete Alpine implementation - prerequisites + Docker + OpenRC, not just partial support
4. Future-proof - won’t need updating when Docker repos are added for new Debian releases

Verification

The implementation follows the exact requirements from #8154:

• ✅ Debian 13 (trixie) validation support
• ✅ Docker installation with intelligent fallback
• ✅ Alpine Linux support (bonus feature)
• ✅ Unit tests included

/claim #8154