feat(announcements,messaging,notifications): 实现所有长期问题 — SSE 实时推送 + 通知日志持久化 + 优先级/归档 + 消息星标/草稿 + 公告已读回执/置顶 + 分类筛选/桌面推送 + 测试覆盖

P1-8 通知实时推送（SSE）:
- 新增 /api/notifications/stream SSE 端点（15 秒推送，5 分钟超时）
- 新增 useNotificationStream Hook（SSE + 轮询降级）
- NotificationDropdown 改用 SSE 实时推送

P2-12 测试覆盖:
- notifications/dispatcher.test.ts（6 个测试，渠道选择逻辑）
- notifications/channels/in-app-channel.test.ts（9 个测试，类型映射）
- messaging/schema.test.ts（34 个测试，Zod 校验）
- tests/e2e/messages.spec.ts（消息模块 E2E 测试）
- vitest.unit.config.ts 添加 server-only stub

P2-13a 通知发送日志持久化:
- 新增 notification_logs 表（userId/title/channel/status/messageId/error/sentAt）
- logNotificationSend 改为 async 写入 DB（失败降级 console）
- dispatcher 传递 payload 用于持久化

P2-13b 通知优先级和归档:
- messageNotifications 表新增 priority（low/normal/high/urgent）和 isArchived 字段
- getNotifications 支持归档和优先级筛选
- 新增 archiveNotificationAction
- NotificationList 显示优先级 Badge 和归档按钮

P2-13c 消息星标和草稿:
- messages 表新增 isStarred 字段
- 新增 message_drafts 表
- 新增 toggleMessageStar + 草稿 CRUD Server Actions
- 新增 5 个草稿 data-access 函数

P2-13d 公告已读回执和置顶:
- announcements 表新增 isPinned 字段
- 新增 announcement_reads 表（唯一索引保证幂等）
- 新增 toggleAnnouncementPinAction + markAnnouncementAsReadAction
- getAnnouncements 排序置顶优先

P2-13e 通知分类筛选和桌面推送:
- NotificationList 添加按类型筛选按钮组
- 新增 useDesktopNotifications Hook（浏览器 Notification API）
- NotificationDropdown 集成桌面推送（新通知触发）

架构图同步:
- 004 和 005 均已更新（新增表、Action、Hook、组件描述）

src/shared/i18n/messages/en/notifications.json

@@ -10,7 +10,9 @@
     "markRead": "Mark as read",
     "markAllRead": "Mark all as read",
     "viewAll": "View all notifications",
-    "view": "View"
+    "view": "View",
+    "archive": "Archive",
+    "unarchive": "Unarchive"
   },
   "type": {
     "message": "Message",
@@ -18,18 +20,30 @@
     "homework": "Homework",
     "grade": "Grade"
   },
+  "filter": {
+    "all": "All"
+  },
+  "priority": {
+    "low": "Low",
+    "normal": "Normal",
+    "high": "High",
+    "urgent": "Urgent"
+  },
   "status": {
     "new": "New"
   },
   "empty": {
     "noNotifications": "No notifications",
     "noNotificationsDesc": "You have no notifications yet.",
-    "noNotificationsDropdown": "No notifications"
+    "noNotificationsDropdown": "No notifications",
+    "noFilterResults": "No results",
+    "noFilterResultsDesc": "No notifications match the current filter."
   },
   "messages": {
     "allMarkedRead": "All notifications marked as read",
     "notificationMarkedRead": "Notification marked as read",
-    "markReadFailed": "Failed to mark as read"
+    "markReadFailed": "Failed to mark as read",
+    "archiveFailed": "Archive failed"
   },
   "error": {
     "loadFailed": "Failed to load notifications",