M10 (task 2013): integrated AppImage — app self-integration (OOBE + Account toggle)

The Linux AppImage can now install itself into the applications menu, so it behaves
like an installed app instead of a loose file.

- Rust (desktop/src-tauri/src/integration.rs): integration_status / integrate_desktop
  / unintegrate_desktop commands — detect $APPIMAGE, copy the AppImage to
  ~/Applications, write ~/.local/share/applications/thoughtsync.desktop + embedded
  icon, update-desktop-database. Registered in lib.rs.
- Frontend: withGlobalTauri exposes window.__TAURI__.core.invoke; desktop/bridge.ts
  (isDesktop + typed invoke, NO @tauri-apps/api dep -> web bundle unaffected);
  DesktopIntegrationPrompt (first-run OOBE, remembered) mounted in App.vue;
  AccountView "Desktop app" add/remove control. All desktop-guarded -> no-ops on web.
- desktop.yml: upload the .deb + .AppImage as a run artifact (continue-on-error) so
  the build is downloadable for hand-testing.

Verified by CI: ci.yml (vue-tsc) for the frontend, desktop.yml (cargo + tauri build)
for the Rust + AppImage.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FRgehjoz7Yv8LkUfADxACm

desktop/src-tauri/src/lib.rs

@@ -1,13 +1,21 @@
 //! ThoughtSync desktop (Tauri v2).
 //!
-//! The window loads the shared Vue 3 frontend (`../../frontend`). Today this is the
-//! shell that boots the UI; the Rust core will own the on-device SQLite store
-//! (M10.4) and the opt-in sync engine (M10.7), which the frontend reaches through
-//! the `frontend/src/adapters/` seam (M10.3) over Tauri `invoke`.
+//! The window loads the shared Vue 3 frontend (`../../frontend`). The Rust core will
+//! own the on-device SQLite store (M10.4) and the opt-in sync engine (M10.7), which
+//! the frontend reaches through the `frontend/src/adapters/` seam (M10.3) over Tauri
+//! `invoke`. Today it exposes desktop integration (menu-entry install for the Linux
+//! AppImage) and boots the UI.
+
+mod integration;
 
 #[cfg_attr(mobile, tauri::mobile_entry_point)]
 pub fn run() {
     tauri::Builder::default()
+        .invoke_handler(tauri::generate_handler![
+            integration::integration_status,
+            integration::integrate_desktop,
+            integration::unintegrate_desktop,
+        ])
         .run(tauri::generate_context!())
         .expect("error while running the ThoughtSync desktop app");
 }