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>

app/services/auth.py

@@ -0,0 +1,39 @@
+from flask import session
+from functools import wraps
+from flask import jsonify
+import base64
+
+def _decrypt_password(encrypted: str) -> str:
+    """Decode base64 encoded password from session."""
+    return base64.b64decode(encrypted.encode()).decode()
+
+def get_current_user():
+    """Get current authenticated user info from session."""
+    if 'username' not in session:
+        return None
+    
+    return {
+        'username': session['username'],
+        'password': _decrypt_password(session['password']),
+        'is_admin': session.get('is_admin', False)
+    }
+
+def require_auth(f):
+    """Decorator to require authentication for a route."""
+    @wraps(f)
+    def decorated_function(*args, **kwargs):
+        if 'username' not in session:
+            return jsonify({'error': 'Authentication required'}), 401
+        return f(*args, **kwargs)
+    return decorated_function
+
+def require_admin(f):
+    """Decorator to require admin privileges for a route."""
+    @wraps(f)
+    def decorated_function(*args, **kwargs):
+        if 'username' not in session:
+            return jsonify({'error': 'Authentication required'}), 401
+        if not session.get('is_admin', False):
+            return jsonify({'error': 'Admin privileges required'}), 403
+        return f(*args, **kwargs)
+    return decorated_function