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).

desktop/resources/README.md

@@ -0,0 +1,13 @@
+# desktop/resources
+
+App + tray icons for electron-builder packaging.
+
+Required for `npm run dist:mac` / `dist:win` (P1 packaging, not needed for dev/typecheck/tests):
+
+- `icon.icns` — macOS app icon (1024×1024 source, `.icns`).
+- `icon.ico` — Windows app icon (256×256 `.ico`).
+- `trayTemplate.png` / `trayTemplate@2x.png` — menubar/tray icon (macOS template image, monochrome).
+
+Generate from `../../public/icon.svg` (the existing PWA icon) with any icon toolchain
+(e.g. `electron-icon-builder`, or `iconutil` on macOS). These are binary assets and
+are intentionally not committed as placeholders — add them before the first packaged build.