Add the GTK home screen, local account store, daemon gRPC wrapper, and embedded Linux daemon startup path so the Linux app follows the Apple client UX and daemon boundary.
Document the GTK parity expectations and update the daemon IPC and Tailnet BEPs with the cross-platform client model.
#238 Add AppImage build support
Implements
- Downgrade to libadwaita 1.3 for wider distro support
- Add build script, workflow, and docs for AppImage
- Add build docs for Debian (apt) and Void Linux
- Building AppImage in CI
