feat: 重新设计公告系统为Header铃铛通知

- 新增 AnnouncementBell 组件，支持 Modal 弹窗和 Markdown 渲染
- 移除 Dashboard 横幅和独立公告页面
- 铃铛位置在 Header 文档按钮左侧，显示未读红点
- 支持点击查看详情、标记已读、全部已读等操作
- 完善国际化，移除所有硬编码中文
- 修复 AnnouncementTargetingEditor watch 循环问题

frontend/pnpm-lock.yaml

@@ -20,12 +20,18 @@ importers:
       chart.js:
         specifier: ^4.4.1
         version: 4.5.1
+      dompurify:
+        specifier: ^3.3.1
+        version: 3.3.1
       driver.js:
         specifier: ^1.4.0
         version: 1.4.0
       file-saver:
         specifier: ^2.0.5
         version: 2.0.5
+      marked:
+        specifier: ^17.0.1
+        version: 17.0.1
       pinia:
         specifier: ^2.1.7
         version: 2.3.1(typescript@5.6.3)(vue@3.5.26(typescript@5.6.3))
@@ -48,6 +54,9 @@ importers:
         specifier: ^0.18.5
         version: 0.18.5
     devDependencies:
+      '@types/dompurify':
+        specifier: ^3.0.5
+        version: 3.2.0
       '@types/file-saver':
         specifier: ^2.0.7
         version: 2.0.7
@@ -1460,6 +1469,10 @@ packages:
   '@types/debug@4.1.12':
     resolution: {integrity: sha512-vIChWdVG3LG1SMxEvI/AK+FWJthlrqlTu7fbrlywTkkaONwk/UAGaULXRlf8vkzFBLVm0zkMdCquhL5aOjhXPQ==}
 
+  '@types/dompurify@3.2.0':
+    resolution: {integrity: sha512-Fgg31wv9QbLDA0SpTOXO3MaxySc4DKGLi8sna4/Utjo4r3ZRPdCt4UQee8BWr+Q5z21yifghREPJGYaEOEIACg==}
+    deprecated: This is a stub types definition. dompurify provides its own type definitions, so you do not need this installed.
+
   '@types/estree-jsx@1.0.5':
     resolution: {integrity: sha512-52CcUVNFyfb1A2ALocQw/Dd1BQFNmSdkuC3BkZ6iqhdMfQz7JWOFRuJFloOzjk+6WijU56m9oKXFAXc7o3Towg==}
 
@@ -5901,6 +5914,10 @@ snapshots:
     dependencies:
       '@types/ms': 2.1.0
 
+  '@types/dompurify@3.2.0':
+    dependencies:
+      dompurify: 3.3.1
+
   '@types/estree-jsx@1.0.5':
     dependencies:
       '@types/estree': 1.0.8