fix: blurhash cache miss, design dropdown visibility + add Hauptwörter panel

- DrawCanvas: call onImageLoad for cached images (fixes permanent blur)
- DrawIt: reset imageLoaded immediately on navigation (shows blur right away)
- Design dropdown: always visible when picture loaded, no longer gated on designOptions or objects count
- Fertigstellen: always visible when picture loaded, disabled when no objects
- Hauptwörter: new panel above object list for picture-level words (db_words_db_pictures)
- Backend: DELETE /api/directus/db-pictures/<id>/words/<junction_id>

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

app.py

@@ -1814,6 +1814,13 @@ def directus_db_picture_words(pic_id):
         return jsonify({"ok": True, "saved": saved})
 
 
+@app.route("/api/directus/db-pictures/<pic_id>/words/<junction_id>", methods=["DELETE"])
+def directus_db_picture_word_delete(pic_id, junction_id):
+    token = request.headers.get("Authorization", "")
+    _directus("DELETE", f"/items/db_words_db_pictures/{junction_id}", token)
+    return jsonify({"ok": True})
+
+
 @app.route("/api/directus/db-objects/<obj_id>/pairs", methods=["GET", "POST"])
 def directus_db_object_pairs(obj_id):
     token = request.headers.get("Authorization", "")