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/routes/auth.py

@@ -0,0 +1,72 @@
+from flask import Blueprint, request, jsonify, session
+from app.services.nextcloud import NextcloudClient
+from config import Config
+import base64
+
+bp = Blueprint('auth', __name__, url_prefix='/api/auth')
+
+def _encrypt_password(password: str) -> str:
+    """Simple base64 encoding for password storage in session."""
+    return base64.b64encode(password.encode()).decode()
+
+def _decrypt_password(encrypted: str) -> str:
+    """Decode base64 encoded password from session."""
+    return base64.b64decode(encrypted.encode()).decode()
+
+@bp.route('/login', methods=['POST'])
+def login():
+    """Authenticate user against Nextcloud."""
+    data = request.get_json()
+    
+    if not data or 'username' not in data or 'password' not in data:
+        return jsonify({'error': 'Username and password required'}), 400
+    
+    username = data['username'].strip()
+    password = data['password']
+    
+    if not username or not password:
+        return jsonify({'error': 'Username and password cannot be empty'}), 400
+    
+    try:
+        # Validate credentials by attempting to connect to Nextcloud
+        nc_client = NextcloudClient(Config.NEXTCLOUD_URL, username, password)
+        
+        if not nc_client.verify_credentials():
+            return jsonify({'error': 'Invalid username or password'}), 401
+        
+        # Check if user is admin
+        is_admin = nc_client.check_admin()
+        
+        # Store credentials in session
+        session['username'] = username
+        session['password'] = _encrypt_password(password)
+        session['is_admin'] = is_admin
+        
+        return jsonify({
+            'success': True,
+            'username': username,
+            'is_admin': is_admin
+        }), 200
+        
+    except Exception as e:
+        return jsonify({'error': f'Authentication failed: {str(e)}'}), 500
+
+@bp.route('/logout', methods=['POST'])
+def logout():
+    """Clear user session."""
+    session.clear()
+    return jsonify({'success': True}), 200
+
+@bp.route('/status', methods=['GET'])
+def status():
+    """Check current authentication status."""
+    if 'username' in session:
+        return jsonify({
+            'authenticated': True,
+            'username': session['username'],
+            'is_admin': session.get('is_admin', False)
+        }), 200
+    else:
+        return jsonify({
+            'authenticated': False
+        }), 200