Add NextSnap PWA with photo gallery viewer and continuous capture

Offline-first photo capture app for Nextcloud with:
- Camera capture with continuous mode (auto-reopens after each photo)
- File browser with fullscreen image gallery, swipe navigation, and rename
- Upload queue with background sync engine
- Admin panel for Nextcloud user management
- Service worker for offline-first caching (v13)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

README.md

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+# NextSnap
+
+Offline-first photo capture web app for Nextcloud.
+
+## Quick Start
+
+### Development
+
+```bash
+python3 -m venv venv
+source venv/bin/activate
+pip install -r requirements.txt
+python run.py
+```
+
+Visit http://localhost:5000/api/health to verify the server is running.
+
+### Docker Deployment
+
+```bash
+export SECRET_KEY="your-secret-key-here"
+export NEXTCLOUD_URL="https://your-nextcloud-instance.com"
+docker-compose up -d
+```
+
+## Architecture
+
+- **Backend**: Flask + Gunicorn
+- **Frontend**: Vanilla JavaScript (no framework)
+- **Offline Storage**: IndexedDB via Dexie.js
+- **Service Worker**: For offline-first capabilities
+- **Nextcloud Integration**: WebDAV API for file operations
+
+## Build Order
+
+See `nextsnap.md` for the complete specification and phased implementation plan.