feat: drag-to-reorder table groups in zone tabs

Backend:
  - tables.py: PUT /api/tables/groups/reorder accepts an ordered list
    of group IDs and updates sort_order accordingly

Frontend (TablesConfigTab):
  - Zone tabs are now draggable for group tabs (not All/Ungrouped)
  - HTML5 drag-and-drop with visual drop-target highlight and a
    grab cursor; fires reorderGroups mutation on drop

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

local_backend/routers/tables.py

@@ -1,4 +1,4 @@
-from fastapi import APIRouter, Depends, HTTPException, status
+from fastapi import APIRouter, Depends, HTTPException, status, Body
 from sqlalchemy.orm import Session
 from typing import List
 
@@ -36,6 +36,13 @@ def create_group(body: TableGroupCreate, db: Session = Depends(get_db), user: Us
     return group
 
 
+@router.put("/groups/reorder", status_code=status.HTTP_204_NO_CONTENT)
+def reorder_groups(body: List[int] = Body(...), db: Session = Depends(get_db), user: User = Depends(require_manager)):
+    for idx, group_id in enumerate(body):
+        db.query(TableGroup).filter(TableGroup.id == group_id).update({"sort_order": idx})
+    db.commit()
+
+
 @router.put("/groups/{group_id}", response_model=TableGroupOut)
 def update_group(group_id: int, body: TableGroupUpdate, db: Session = Depends(get_db), user: User = Depends(require_manager)):
     group = db.query(TableGroup).filter(TableGroup.id == group_id).first()