feat: 支局长可删除用户 + 清理重复蓝浩博

- 新增 DELETE /api/users/{id} (require_director, 不能删自己)
- 用户管理页新增「删除」按钮(仅支局长可见)
- 删除重复的分管领导蓝浩博

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

backend/app/api/users.py

@@ -122,3 +122,23 @@ async def update_user_wecom(
         "name": user.name,
         "wecom_userid": user.wecom_userid,
     }
+
+
+@router.delete("/{user_id}")
+async def delete_user(
+    user_id: str,
+    current_user: dict = Depends(require_director),
+    db: AsyncSession = Depends(get_db),
+):
+    """Director deletes a user. Cannot delete self."""
+    if user_id == current_user["user_id"]:
+        raise HTTPException(status_code=400, detail="不能删除自己")
+
+    result = await db.execute(select(User).where(User.id == uuid.UUID(user_id)))
+    user = result.scalar_one_or_none()
+    if not user:
+        raise HTTPException(status_code=404, detail="User not found")
+
+    await db.delete(user)
+    await db.commit()
+    return {"detail": "deleted", "name": user.name}