fix: Design-PATCH fehlte Bearer-Token + Race Condition bei Fertigstellen

- Neues updateDbPicture() in api.ts mit korrektem Bearer-Header
- Design-onChange nutzt updateDbPicture statt rohem fetch (kein Bearer-Bug mehr)
- finishPicture sendet status + design in einem PATCH (kein Race Condition)
- app.py: get_json(force=True, silent=True) für db-pictures PATCH

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app.py

@@ -1730,7 +1730,7 @@ def directus_db_pictures_design_options():
 @app.route("/api/directus/db-pictures/<pic_id>", methods=["PATCH"])
 def directus_db_picture_patch(pic_id):
     token = request.headers.get("Authorization", "")
-    data, status = _directus("PATCH", f"/items/db_pictures/{pic_id}", token, body=request.get_json())
+    data, status = _directus("PATCH", f"/items/db_pictures/{pic_id}", token, body=request.get_json(force=True, silent=True))
     return jsonify(data), status