fix: 修复机房管理和机柜管理页面的重复选择框问题

- 删除RoomManagement中手动定义的Checkbox选择列
- 删除RackManagement中手动定义的Checkbox选择列
- 保留rowSelection属性，使用Ant Design内置的选择功能

frontend/src/pages/RackManagement.jsx

@@ -462,35 +462,6 @@ function RackManagement() {
   }), [racks]);
 
   const tableColumns = [
-    {
-      title: (
-        <Checkbox
-          checked={selectedRackIds.length === filteredRacks.length && filteredRacks.length > 0}
-          indeterminate={selectedRackIds.length > 0 && selectedRackIds.length < filteredRacks.length}
-          onChange={(e) => {
-            if (e.target.checked) {
-              setSelectedRackIds(filteredRacks.map(r => r.rackId));
-            } else {
-              setSelectedRackIds([]);
-            }
-          }}
-        />
-      ),
-      key: 'selection',
-      width: 50,
-      render: (_, record) => (
-        <Checkbox
-          checked={selectedRackIds.includes(record.rackId)}
-          onChange={(e) => {
-            if (e.target.checked) {
-              setSelectedRackIds([...selectedRackIds, record.rackId]);
-            } else {
-              setSelectedRackIds(selectedRackIds.filter(id => id !== record.rackId));
-            }
-          }}
-        />
-      )
-    },
     {
       title: '机柜信息',
       key: 'rackInfo',

frontend/src/pages/RoomManagement.jsx

@@ -378,35 +378,6 @@ function RoomManagement() {
   }), [rooms]);
 
   const tableColumns = [
-    {
-      title: (
-        <Checkbox
-          checked={selectedRoomIds.length === filteredRooms.length && filteredRooms.length > 0}
-          indeterminate={selectedRoomIds.length > 0 && selectedRoomIds.length < filteredRooms.length}
-          onChange={(e) => {
-            if (e.target.checked) {
-              setSelectedRoomIds(filteredRooms.map(r => r.roomId));
-            } else {
-              setSelectedRoomIds([]);
-            }
-          }}
-        />
-      ),
-      key: 'selection',
-      width: 50,
-      render: (_, record) => (
-        <Checkbox
-          checked={selectedRoomIds.includes(record.roomId)}
-          onChange={(e) => {
-            if (e.target.checked) {
-              setSelectedRoomIds([...selectedRoomIds, record.roomId]);
-            } else {
-              setSelectedRoomIds(selectedRoomIds.filter(id => id !== record.roomId));
-            }
-          }}
-        />
-      )
-    },
     {
       title: '机房信息',
       key: 'roomInfo',