fix: restore tree root node (📁 根目录)

wwwroot/knowledge_bases_list/get_tree_data.dspy

@@ -8,7 +8,10 @@ async with db.sqlorContext(dbname) as sor:
         recs = await sor.sqlExe(
             "SELECT id, '' as parentid, content as label FROM document_chunks WHERE kb_id=${kb_id}$ AND chunk_type='directory' AND (description IS NULL OR description='') ORDER BY content",
             {"kb_id": kb_id})
-        return [dict(r) for r in recs]
+        result = [{"id": "__root__", "parentid": "", "label": "📁 根目录"}]
+        for r in recs:
+            result.append({"id": r.id, "parentid": r.parentid, "label": r.label})
+        return result
     else:
         recs = await sor.sqlExe(
             "SELECT id, description as parentid, content as label FROM document_chunks WHERE kb_id=${kb_id}$ AND chunk_type='directory' AND description=${id}$ ORDER BY content",