Documentation updates across guides and function references:
- Added var_gpu and var_tun configuration entries to CONFIGURATION_REFERENCE (GPU passthrough and TUN/TAP support), including features and prerequisites.
- Fixed repository URLs throughout UNATTENDED_DEPLOYMENTS and examples: replaced community-scripts/ProxmoxVED with community-scripts/ProxmoxVE and updated curl usage to the new paths.
- Added an "Advanced Configuration Variables" table and examples (var_os, var_version, var_gpu, var_tun, var_nesting) to UNATTENDED_DEPLOYMENTS; adjusted sample apps, hostnames, and container mappings in batch examples.
- Switched API endpoints in API_FUNCTIONS_REFERENCE and API_USAGE_EXAMPLES from http://api.community-scripts.org to https://api.community-scripts.org.
- Expanded BUILD_FUNC_FUNCTIONS_REFERENCE with container resource/ID management helper descriptions (validate_container_id, get_valid_container_id, maxkeys_check, get_current_ip, update_motd_ip).
- Large edits to TOOLS_FUNC_FUNCTIONS_REFERENCE: renamed/refactored helper signatures and docs (pkg_install -> install_packages_with_retry, pkg_update -> upgrade_packages_with_retry), added new tooling functions (fetch_and_deploy_gh_release, check_for_gh_release, prepare_repository_setup, verify_tool_version) and updated examples and feature notes.
- Updated vm/README.md to list additional VM scripts (new and reorganized examples).
These are documentation-only changes to clarify configuration options, correct links and endpoints, and expand the reference material for tooling and build helpers.
- 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.
