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

.forgejo/workflows/desktop.yml

@@ -66,3 +66,16 @@ jobs:
       - name: Tauri build (deb + AppImage)
         run: cargo tauri build --config '{"build":{"beforeBuildCommand":""}}'
         working-directory: desktop/src-tauri
+
+      # Make the built .deb + .AppImage downloadable from the run (for hand-testing).
+      # continue-on-error: the Forgejo artifact backend may not be configured yet; a
+      # failed upload must not fail the build itself.
+      - name: Upload bundles
+        continue-on-error: true
+        uses: actions/upload-artifact@v4
+        with:
+          name: thoughtsync-linux
+          path: |
+            desktop/src-tauri/target/release/bundle/appimage/*.AppImage
+            desktop/src-tauri/target/release/bundle/deb/*.deb
+          if-no-files-found: warn