fix: OnlyOffice Callback JWT-Validierung + Speichern

Problem: OnlyOffice sendete JWT-Token im Callback-Request und im
Body, unser Endpoint hat das ignoriert -> Speichern schlug fehl.

Fix:
- Callback validiert OnlyOffice JWT aus Authorization-Header
- Callback entpackt JWT-wrapped Body (OnlyOffice wraps den Body
  in einen JWT-Token wenn JWT_ENABLED=true)
- Download der gespeicherten Datei sendet JWT-Header mit
- Besseres Error-Logging mit Traceback

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

backend/app/api/office.py

@@ -422,14 +422,35 @@ def onlyoffice_callback():
     """Callback from OnlyOffice when document is saved."""
     import urllib.request
 
+    # Validate OnlyOffice JWT token if JWT is enabled
+    jwt_secret = os.environ.get('JWT_SECRET_KEY', '')
+    if jwt_secret:
+        import jwt as pyjwt
+        auth_header = request.headers.get('Authorization', '')
+        if auth_header.startswith('Bearer '):
+            oo_token = auth_header[7:]
+            try:
+                pyjwt.decode(oo_token, jwt_secret, algorithms=['HS256'])
+            except Exception as e:
+                print(f'[OnlyOffice Callback] JWT validation failed: {e}')
+                return jsonify({'error': 1}), 200
+
     callback_key = request.args.get('key', '')
     file_id_str = AppSettings.get(f'oo_callback_{callback_key}', '')
 
     if not file_id_str:
         return jsonify({'error': 1}), 200  # OnlyOffice expects {"error": 0} for success
 
+    # OnlyOffice may wrap the body in a JWT token
     data = request.get_json()
-    status = data.get('status', 0)
+    if data and 'token' in data and jwt_secret:
+        import jwt as pyjwt
+        try:
+            data = pyjwt.decode(data['token'], jwt_secret, algorithms=['HS256'])
+        except Exception:
+            pass
+
+    status = data.get('status', 0) if data else 0
 
     # Status 2 = document ready for saving, 6 = force save
     if status in (2, 6):
@@ -443,7 +464,15 @@ def onlyoffice_callback():
                     filepath = Path(current_app.config['UPLOAD_PATH']) / str(f.owner_id) / f.storage_path
 
                     # Download the saved document from OnlyOffice
-                    urllib.request.urlretrieve(download_url, str(filepath))
+                    req = urllib.request.Request(download_url)
+                    if jwt_secret:
+                        # OnlyOffice may require JWT for download too
+                        import jwt as pyjwt
+                        dl_token = pyjwt.encode({'url': download_url}, jwt_secret, algorithm='HS256')
+                        req.add_header('Authorization', f'Bearer {dl_token}')
+                    with urllib.request.urlopen(req) as resp, open(str(filepath), 'wb') as out:
+                        import shutil
+                        shutil.copyfileobj(resp, out)
 
                     # Update metadata
                     f.size = os.path.getsize(str(filepath))
@@ -455,7 +484,9 @@ def onlyoffice_callback():
                     f.updated_at = datetime.now(timezone.utc)
                     db.session.commit()
             except Exception as e:
-                print(f'[OnlyOffice Callback] Error: {e}')
+                print(f'[OnlyOffice Callback] Save error: {e}')
+                import traceback
+                traceback.print_exc()
                 return jsonify({'error': 1}), 200
 
     # Status 4 = closed without changes