feat(pos): Capacitor mobile app setup — Android + iOS wrapper

Set up Capacitor to wrap the Nexus POS web app as a native mobile app.
The app loads from the remote server URL so no bundling is needed.
Includes native-bridge.js for camera, push notifications, haptics,
and status bar integration when running inside the native shell.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

pos/templates/pos.html

@@ -9,6 +9,7 @@
   <link rel="stylesheet" href="/pos/static/css/chat.css" />
   <link rel="manifest" href="/pos/static/pwa/manifest.json" />
   <meta name="theme-color" content="#F5A623" />
+  <script src="/pos/static/js/native-bridge.js"></script>
 
   <style>
     /* =====================================================================