fix: Save-Endpoints feuern SSE-Event - Web-Edits synchronisieren sich

/files/<id>/save (Text/HTML/Spreadsheet) und der OnlyOffice-
Callback aktualisierten Inhalt + Checksum, riefen aber
notify_file_change nicht auf. Der Client bekam dadurch keinen
SSE-Trigger und merkte die neue Server-Version erst beim naechsten
30s-Fallback-Sync - wenn ueberhaupt.

Jetzt: beide Endpoints emittieren 'updated' an Owner + Share-
Empfaenger, Desktop- und Web-Clients reagieren sofort.

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

backend/app/api/office.py

@@ -8,9 +8,10 @@ from flask import request, jsonify, current_app, send_file
 
 from app.api import api_bp
 from app.api.auth import token_required
-from app.api.files import _get_file_or_403
+from app.api.files import _get_file_or_403, _share_recipients
 from app.extensions import db
 from app.models.settings import AppSettings
+from app.services.events import notify_file_change
 
 
 @api_bp.route('/files/<int:file_id>/preview', methods=['GET'])
@@ -219,6 +220,8 @@ def save_file(file_id):
         f.updated_at = datetime.now(timezone.utc)
         db.session.commit()
 
+        notify_file_change(f.owner_id, f.id, 'updated',
+                           shared_with=_share_recipients(f))
         return jsonify({'message': 'Gespeichert', 'size': f.size}), 200
     except Exception as e:
         return jsonify({'error': f'Speichern fehlgeschlagen: {str(e)}'}), 500
@@ -482,6 +485,8 @@ def onlyoffice_callback():
                         f.checksum = h.hexdigest()
                         f.updated_at = datetime.now(timezone.utc)
                         db.session.commit()
+                        notify_file_change(f.owner_id, f.id, 'updated',
+                                           shared_with=_share_recipients(f))
                         print(f'[OnlyOffice Callback] File saved: {f.name} ({f.size} bytes)')
 
         # Status 2, 4, 6: cleanup