已完善个人教学日历订阅。

主要能力：
教师、学生可在“我的课表”启用订阅、复制 URL、唤起日历客户端或下载一次性 ICS。
自动覆盖固定课程、调停课后的最新安排、考试/监考、补考，以及灵活课程提醒。
采用独立随机订阅标识和 HMAC 签名；重置或停用后旧地址立即失效。
支持 ETag 条件请求和一小时刷新提示，减少日历客户端重复同步。
订阅地址按实际前端 API 地址生成，兼容独立部署域名。
已增加窄屏弹窗最大宽度和纵向操作布局。

src/Jiaowu.Api/Infrastructure/Persistence/DevelopmentSqliteMigrator.cs

@@ -50,6 +50,8 @@ public sealed class DevelopmentSqliteMigrator(
         "20260726_27_academic_term_archiving";
     private const string CourseSelectionWaitlistMigration =
         "20260726_28_course_selection_waitlist";
+    private const string PersonalCalendarSubscriptionMigration =
+        "20260726_29_personal_calendar_subscription";
 
     public async Task MigrateAsync(CancellationToken cancellationToken = default)
     {
@@ -359,6 +361,21 @@ public sealed class DevelopmentSqliteMigrator(
             CourseSelectionWaitlistMigration,
             courseSelectionWaitlistExists ? [] : CourseSelectionWaitlistStatements,
             cancellationToken);
+
+        var personalCalendarSubscriptionExists = await db.Database
+            .SqlQueryRaw<int>(
+                """
+                SELECT COUNT(*) AS "Value"
+                FROM pragma_table_info('AspNetUsers')
+                WHERE name = 'CalendarSubscriptionStamp'
+                """)
+            .AnyAsync(value => value > 0, cancellationToken);
+        await ApplyMigrationAsync(
+            PersonalCalendarSubscriptionMigration,
+            personalCalendarSubscriptionExists
+                ? []
+                : PersonalCalendarSubscriptionStatements,
+            cancellationToken);
     }
 
     private async Task ApplyMigrationAsync(
@@ -1616,6 +1633,18 @@ public sealed class DevelopmentSqliteMigrator(
         """
     ];
 
+    private static readonly string[] PersonalCalendarSubscriptionStatements =
+    [
+        """
+        ALTER TABLE "AspNetUsers"
+        ADD COLUMN "CalendarSubscriptionStamp" TEXT NULL;
+        """,
+        """
+        ALTER TABLE "AspNetUsers"
+        ADD COLUMN "CalendarSubscriptionCreatedAt" TEXT NULL;
+        """
+    ];
+
     private static readonly string[] CourseAdjustmentsStatements =
     [
         """