- Add storePlainTextPassword setting in SettingsCore and SettingsModel
- Add UI switch in CarddavSettingsLayout.qml to toggle plain text password
- Allow multiple CardDAV accounts by setting showAddButton = true
- Add CardDAV troubleshooting documentation in README.md
This fixes CardDAV synchronization with Nextcloud/WebDAV servers that use
HTTP Basic Authentication, which requires plain text passwords instead
of the default HA1 hash storage.
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>