feat: object label per object + {obj:UUID} sentence placeholders

- Annotate: per-object single label input (M2M via db_objects_db_words), auto-save on blur, remove picture-level word section
- Generate: object chips insert {obj:UUID} at cursor position in question/statement textarea
- Live preview resolves {obj:UUID} → actual object label
- PairsList display also resolves placeholders
- Remove F/A/B word chip system from pair form (replaced by object placeholders)
- Backend: POST /api/directus/db-objects/<id>/words replaces existing word with single label

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

app.py

@@ -1895,31 +1895,45 @@ def directus_db_object_pairs(obj_id):
         return jsonify({"ok": True, "pair_id": pair_id, "statement_id": stmt_id, "question_id": q_id})
 
 
-@app.route("/api/directus/db-objects/<obj_id>/words", methods=["GET"])
+@app.route("/api/directus/db-objects/<obj_id>/words", methods=["GET", "POST"])
 def directus_db_object_words(obj_id):
     """Gibt alle db_words zurück, die via db_objects_db_words mit dem Objekt verknüpft sind."""
     token = request.headers.get("Authorization", "")
-    data, s = _directus(
-        "GET",
-        f"/items/db_objects_db_words?filter[db_objects_id][_eq]={obj_id}"
-        f"&fields=id,db_words_id.id,db_words_id.titel_de,db_words_id.level,db_words_id.status&limit=500",
-        token,
-    )
-    if s != 200:
-        return jsonify({"data": []})
-    items = []
-    for entry in (data.get("data") or []):
-        word = entry.get("db_words_id") or {}
-        if not isinstance(word, dict) or not word.get("id"):
-            continue
-        if word.get("status") == "archived":
-            continue
-        items.append({
-            "word_id": word["id"],
-            "titel_de": word.get("titel_de", ""),
-            "level": word.get("level") or 50,
-        })
-    return jsonify({"data": items})
+    if request.method == "GET":
+        data, s = _directus(
+            "GET",
+            f"/items/db_objects_db_words?filter[db_objects_id][_eq]={obj_id}"
+            f"&fields=id,db_words_id.id,db_words_id.titel_de,db_words_id.level,db_words_id.status&limit=500",
+            token,
+        )
+        if s != 200:
+            return jsonify({"data": []})
+        items = []
+        for entry in (data.get("data") or []):
+            word = entry.get("db_words_id") or {}
+            if not isinstance(word, dict) or not word.get("id"):
+                continue
+            if word.get("status") == "archived":
+                continue
+            items.append({
+                "word_id": word["id"],
+                "titel_de": word.get("titel_de", ""),
+                "level": word.get("level") or 50,
+            })
+        return jsonify({"data": items})
+    else:  # POST — replace with single word
+        body = request.get_json(force=True, silent=True) or {}
+        titel_de = (body.get("titel_de") or "").strip()
+        level = int(body.get("level") or 50)
+        # Delete all existing junctions for this object
+        existing, _ = _directus("GET", f"/items/db_objects_db_words?filter[db_objects_id][_eq]={obj_id}&fields=id&limit=20", token)
+        for e in (existing.get("data") or []):
+            _directus("DELETE", f"/items/db_objects_db_words/{e['id']}", token)
+        if not titel_de:
+            return jsonify({"ok": True, "cleared": True})
+        wid, _ = _find_or_create_db_word(titel_de, level, token)
+        _directus("POST", "/items/db_objects_db_words", token, {"db_objects_id": obj_id, "db_words_id": wid})
+        return jsonify({"ok": True, "word_id": wid})
 
 
 @app.route("/api/directus/db-pairs/<pair_id>", methods=["PATCH", "DELETE"])