- Changed setup_mariadb() to use Debian/Ubuntu distribution packages by default
- Official MariaDB repository only used when specific version is requested
- Added cleanup logic for old/orphaned repository files with apt update
- Added version comparison to prevent downgrades (keeps higher version installed)
- Added automatic fallback to distro packages if repo installation fails
- Extracted _setup_mariadb_runtime_dir() helper function
- Updated all related documentation
This change improves reliability by avoiding MariaDB mirror issues
(HTTPS->HTTP redirects, geographic availability problems) for standard
installations while still allowing specific versions when needed.
