kcms/componentchooser: add option to choose default calendar
Original commit message(s)
- feat(componentchooser): add calendar application selector
Reason for the change
Adds a "Calendar" entry to the Default Applications KCM, allowing users to configure their preferred calendar application. This was previously missing — users had no GUI way to change the default calendar app.
Test plan
- Open System Settings → Default Applications
- Verify "Calendar" entry appears in the Internet section
- Change the calendar application and verify it persists after closing/reopening
- Click "Reset to defaults" and verify the calendar selection resets
- Verify the "View Details" warning works if the selected app doesn't support all relevant MIME types
Screenshots or screen recordings
