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

frontend/src/desktop/bridge.ts

@@ -0,0 +1,38 @@
+// Bridge to the Tauri desktop core. On the web build there is no Tauri runtime, so
+// isDesktop() is false and none of these calls run. Uses the global injected by
+// `withGlobalTauri` (tauri.conf.json), so the shared frontend needs no
+// @tauri-apps/api dependency and the web bundle is unaffected.
+
+interface TauriGlobal {
+  core: { invoke: <T>(cmd: string, args?: Record<string, unknown>) => Promise<T> };
+}
+
+declare global {
+  interface Window {
+    __TAURI__?: TauriGlobal;
+  }
+}
+
+export interface IntegrationStatus {
+  is_appimage: boolean;
+  is_integrated: boolean;
+  appimage_path: string | null;
+}
+
+/** True when running inside the Tauri desktop shell (vs. the web build). */
+export function isDesktop(): boolean {
+  return typeof window !== "undefined" && !!window.__TAURI__;
+}
+
+function invoke<T>(cmd: string, args?: Record<string, unknown>): Promise<T> {
+  const tauri = window.__TAURI__;
+  if (!tauri) return Promise.reject(new Error("Not running in the desktop app."));
+  return tauri.core.invoke<T>(cmd, args);
+}
+
+// Desktop (Linux AppImage) self-integration: add/remove an applications-menu entry.
+export const desktop = {
+  integrationStatus: () => invoke<IntegrationStatus>("integration_status"),
+  integrate: () => invoke<IntegrationStatus>("integrate_desktop"),
+  unintegrate: () => invoke<IntegrationStatus>("unintegrate_desktop"),
+};