feat(提交详情): 点了班级筛选之后，要挪到上面班级下拉去点 × 才能取消——右栏那个班级标签原地变成「取消」

已经在筛这个班时，标签不再消失，填色带 ×，悬停变红，再点一下回到全部班级。手机上顺手关掉详情抽屉。

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

apps/web/src/oj/submission/list.vue

@@ -1037,6 +1037,7 @@ function dayBreak(index: number) {
           :position="position"
           @filter-user="filterUser"
           @filter-class="filterClass"
+          @clear-class="query.className = ''"
           @filter-problem="filterProblem"
           @open-problem="openProblem"
           @rejudge="rejudge"
@@ -1076,6 +1077,7 @@ function dayBreak(index: number) {
           narrow
           @filter-user="(name: string) => ((mobilePane = false), filterUser(name))"
           @filter-class="(name: string) => ((mobilePane = false), filterClass(name))"
+          @clear-class="() => ((mobilePane = false), (query.className = ''))"
           @filter-problem="(id: string) => ((mobilePane = false), filterProblem(id))"
           @open-problem="openProblem"
           @rejudge="rejudge"