feat(clients): scaffold mobile (Capacitor) + desktop (Electron) shells

Plan + decisions in CLIENTS.md (parallel mobile+desktop; desktop = technician
client + existing remote-control agent host; mobile = Capacitor wrap).

- desktop/: Electron technician client — loads the live Connect UI, native
  screen capture via setDisplayMediaRequestHandler, persisted session, external
  links to browser; electron-builder config for Win/Mac/Linux installers.
- mobile/: Capacitor project — server.url loads Connect UI, push/camera/status-bar
  plugins declared, www splash fallback; iOS/Android added via `cap add`.
- Reuses the existing /api/v1 + Bearer auth backend; no web-code changes.
- .gitignore: ignore generated mobile/android, mobile/ios platform dirs.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

desktop/preload.js

@@ -0,0 +1,10 @@
+// Minimal, safe bridge into the web UI. Runs with contextIsolation, so it only exposes a
+// frozen marker the web app can feature-detect against (e.g. to hide the PWA install prompt
+// or prefer native push). No Node APIs are exposed to page JS.
+const { contextBridge } = require('electron');
+
+contextBridge.exposeInMainWorld('__NATIVE__', 'desktop');
+contextBridge.exposeInMainWorld('bizConnectNative', Object.freeze({
+  platform: 'desktop',
+  version: process.env.npm_package_version || '0.1.0',
+}));