* fix: Lazy GTK imports for better pip/pipx compatibility
- Move GTK-dependent imports (tray_indicator) inside main() function
- Import after check_dependencies() so users get helpful error messages
- Update ui/__init__.py to not import tray_indicator at module level
- Update vocalinux/__init__.py to not import GTK-dependent modules
- Improved error messages for pip/pipx users with missing GTK typelibs
- Bump version to 0.2.1-alpha
This fixes the 'Namespace AppIndicator3 not available' error that
pip/pipx users encounter because PyGObject can't find system typelibs.
Closes#47
* test: simplify settings dialog tests
* style: fix lazy import ordering