refactor: merge GNOME config files and make maclike the default

- Merge gnome_common.yml, gnome_winlike.yml, gnome_maclike.yml into single gnome.yml
- Add dfe_ui_mode variable set based on active tag (winlike or maclike)
- Change --all flag default from winlike to maclike (macOS-style dock)
- Remove --force-gnome option (no longer needed with installed-not-running detection)
- Update install.sh and test.sh help text and override logic

Tested on Fedora 42 and Ubuntu 24.04.

Author: Derek