✨ feat: Enhance announcements UX with unread badge, tabbed NoticeModal, and shine animation

• HeaderBar
  - Added dynamic unread badge; click now opens NoticeModal on “System Announcements” tab
  - Passes `defaultTab` and `unreadKeys` props to NoticeModal for contextual behaviour

• NoticeModal
  - Introduced Tabs inside the modal title with Lucide icons (Bell, Megaphone)
  - Displays in-app notice (markdown) and system announcements separately
  - Highlights unread announcements with “shine” text animation
  - Accepts new props `defaultTab`, `unreadKeys` to control initial tab and highlight logic

• CSS (index.css)
  - Implemented `sweep-shine` keyframes and `.shine-text` utility for left-to-right glow
  - Added dark-mode variant for better contrast
  - Ensured cross-browser support with standard `background-clip`

Overall, users now see an unread counter, are directed to new announcements automatically, and benefit from an eye-catching glow effect that works in both light and dark themes.

web/src/i18n/locales/en.json

@@ -1700,5 +1700,6 @@
   "最低充值美元数量": "Minimum recharge dollar amount",
   "充值分组倍率": "Recharge group ratio",
   "充值方式设置": "Recharge method settings",
-  "更新支付设置": "Update payment settings"
+  "更新支付设置": "Update payment settings",
+  "通知": "Notice"
 }