fix: 完善任务导航与结束会话错误处理

- 结束会话 API 异常时显示错误，不导航（可重试）
- 结束会话硬跳转改为软导航 router.push
- TaskForm 创建/更新/取消后跳转任务列表页
- 移除 TaskForm 页面内大标题

src/components/TaskForm.vue

@@ -22,12 +22,6 @@ const priority = ref({
 });
 
 const priorityOptions = [0, 1, 2, 3, 4, 5];
-const pageTitle = computed(() => (route.name === "update-task" ? "更新学习任务" : "创建学习任务"));
-const pageSubtitle = computed(() =>
-  route.name === "update-task"
-    ? "修改任务信息后保存，后续学习会话将使用最新内容"
-    : "填写任务基本信息与优先级维度，帮助系统更好排序"
-);
 
 const createTask = () => {
   request
@@ -40,7 +34,7 @@ const createTask = () => {
     .then((result) => {
       if (result.code === 200) {
         ElMessage.success("创建任务成功");
-        router.back();
+        router.push({ name: "study" });
       } else {
         ElMessage.error("任务创建失败：" + result.message);
       }
@@ -81,7 +75,7 @@ const updateTask = () => {
     .then((result) => {
       if (result.code === 200) {
         ElMessage.success("更新任务成功");
-        router.back();
+        router.push({ name: "study" });
       } else {
         ElMessage.error("任务更新失败：" + result.message);
       }
@@ -90,7 +84,7 @@ const updateTask = () => {
 
 const cancelTask = () => {
   ElMessage.info("已取消操作");
-  router.back();
+  router.push({ name: "study" });
 };
 
 const submitTask = () => {
@@ -126,11 +120,6 @@ const isMobile = computed(() => screenWidth.value <= 900);
 
 <template>
   <section class="task-form-page">
-    <header class="surface-card form-header">
-      <h1 class="page-title">{{ pageTitle }}</h1>
-      <p class="page-subtitle">{{ pageSubtitle }}</p>
-    </header>
-
     <el-form label-position="top" class="surface-card form-shell">
       <div class="group">
         <h3>基础信息</h3>
@@ -195,10 +184,6 @@ const isMobile = computed(() => screenWidth.value <= 900);
   gap: 14px;
 }
 
-.form-header {
-  padding: 20px 22px;
-}
-
 .form-shell {
   padding: 22px;
 }