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/mobile/README.md

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+# Nexus POS — Mobile App Build Guide
+
+## Prerequisites
+- Node.js 18+
+- Android Studio (for Android)
+- Xcode 15+ (for iOS, macOS only)
+
+## Architecture
+
+The Capacitor app loads the POS from the remote server at
+`https://nexus.consultoria-as.com/pos`. This means:
+- The app requires internet on first load.
+- The PWA service worker handles offline caching after that.
+- No HTML/JS/CSS is bundled into the native binary.
+
+## Android Build
+
+```bash
+cd /home/Autopartes/pos
+npx cap sync android
+npx cap open android
+# In Android Studio: Build > Generate Signed APK
+```
+
+## iOS Build
+
+```bash
+cd /home/Autopartes/pos
+npx cap sync ios
+npx cap open ios
+# In Xcode: Product > Archive
+```
+
+## Development
+
+```bash
+npx cap run android --livereload --external
+npx cap run ios --livereload --external
+```
+
+## App Icons & Splash Screens
+
+Place source images in `mobile/resources/`:
+- `icon.png` — 1024x1024 app icon
+- `splash.png` — 2732x2732 splash screen
+
+Then generate platform assets:
+```bash
+npx @capacitor/assets generate
+```