feat(desktop): Electron all-in-one desktop shell (Mac/Windows) embedding the server

Add a `desktop/` Electron app that embeds the existing Node server + node-pty
(all-in-one): the window loads http://127.0.0.1:<port>/ and reuses the frontend
unchanged; other LAN devices can still connect. The server needs zero changes —
startServer(cfg)/loadConfig already support programmatic embedding.

- Pure, unit-tested modules: port, shell, server-config, deep-link, notify-policy,
  notifications, live-poll, prefs, settings-store (94 tests; desktop/src ~97% cov)
- Electron glue: main/window/tray/menu/preload/embedded-server/logger
  (hardened: contextIsolation, sandbox, deny foreign-origin navigation)
- Native value: OS notifications driven by /live-sessions status, tray, deep links
- Packaging (electron-builder -> arm64 .dmg): ships dist/ + public/ + node_modules
  on-disk under Resources so the server resolves its deps from /Applications;
  node-pty rebuilt for the Electron ABI
- Docs: docs/DESKTOP_PLAN.md; PROGRESS_LOG updated

Verified: desktop tsc clean; 1401 tests pass; coverage >=80% (desktop/src 97/95/100/97);
.dmg built and launch-tested on arm64 (server boots, UI serves 200, node-pty loads).

vitest.config.ts

@@ -24,6 +24,20 @@ export default defineConfig({
         'public/title-util.ts',
         'public/voice-commands.ts',
         'public/voice-confirm.ts',
+        // Desktop (Electron) shell: only the PURE logic modules are measured.
+        // The Electron glue (main/window/tray/menu/notifications/preload/
+        // embedded-server/settings-store) is thin, side-effectful wiring around
+        // the electron/native/dist APIs — untestable as a unit and excluded on
+        // the same principle as the thin DOM-wiring public/*.ts above.
+        'desktop/src/port.ts',
+        'desktop/src/shell.ts',
+        'desktop/src/server-config.ts',
+        'desktop/src/deep-link.ts',
+        'desktop/src/notify-policy.ts',
+        'desktop/src/notifications.ts',
+        'desktop/src/live-poll.ts',
+        'desktop/src/prefs.ts',
+        'desktop/src/settings-store.ts',
       ],
       thresholds: {
         lines: 80,