fix: OnlyOffice nutzt internes Docker-Netzwerk + langlebigen Token

Problem: OnlyOffice versuchte Dateien ueber die oeffentliche URL
herunterzuladen (http://selftestcloud...) und bekam 401 weil der
Access-Token nach 15 Min. ablief.

Fix:
- Download-URL und Callback-URL nutzen jetzt die interne Docker-URL
  (http://minicloud:5000) statt die oeffentliche URL
- Eigener 24h-Token fuer OnlyOffice Datei-Zugriff (statt des
  kurzlebigen User-Access-Tokens)
- ONLYOFFICE_INTERNAL_URL konfigurierbar (Default: http://minicloud:5000)

So bleibt der gesamte Dateizugriff zwischen OnlyOffice und Mini-Cloud
im Docker-Netzwerk - schneller und kein externer Roundtrip.

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

backend/app/api/office.py

@@ -1,7 +1,7 @@
 import io
 import os
 import hashlib
-from datetime import datetime, timezone
+from datetime import datetime, timezone, timedelta
 from pathlib import Path
 
 from flask import request, jsonify, current_app, send_file
@@ -353,9 +353,22 @@ def onlyoffice_config(file_id):
     AppSettings.set(f'oo_callback_{callback_key}', str(file_id))
 
     # Build the config
-    # The URLs must be reachable by OnlyOffice server (not the browser)
-    base_url = request.host_url.rstrip('/')
-    token = request.args.get('token', '') or request.headers.get('Authorization', '').replace('Bearer ', '')
+    # Internal URL for OnlyOffice to reach our backend (Docker network)
+    internal_url = os.environ.get('ONLYOFFICE_INTERNAL_URL', 'http://minicloud:5000')
+
+    # Generate a long-lived token for OnlyOffice file access (24h)
+    from app.api.auth import create_access_token
+    import jwt as pyjwt
+    oo_file_token = pyjwt.encode(
+        {
+            'user_id': user.id,
+            'type': 'access',
+            'exp': datetime.now(timezone.utc) + timedelta(hours=24),
+            'iat': datetime.now(timezone.utc),
+        },
+        current_app.config['JWT_SECRET_KEY'],
+        algorithm='HS256',
+    )
 
     config = {
         'available': True,
@@ -365,11 +378,11 @@ def onlyoffice_config(file_id):
                 'fileType': ext,
                 'key': f'{file_id}_{f.checksum or "0"}_{callback_key[:8]}',
                 'title': f.name,
-                'url': f'{base_url}/api/files/{file_id}/download?token={token}',
+                'url': f'{internal_url}/api/files/{file_id}/download?token={oo_file_token}',
             },
             'documentType': doc_type,
             'editorConfig': {
-                'callbackUrl': f'{base_url}/api/files/onlyoffice-callback?key={callback_key}',
+                'callbackUrl': f'{internal_url}/api/files/onlyoffice-callback?key={callback_key}',
                 'mode': 'edit' if can_write else 'view',
                 'lang': 'de',
                 'user': {