✨ 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/index.css

@@ -500,4 +500,32 @@ code {
 
 .components-transfer-selected-item .semi-icon-close:hover {
   color: var(--semi-color-text-0);
+}
+
+/* ==================== 未读通知闪光效果 ==================== */
+@keyframes sweep-shine {
+  0% {
+    background-position: 200% 0;
+  }
+
+  100% {
+    background-position: -200% 0;
+  }
+}
+
+.shine-text {
+  background: linear-gradient(90deg, currentColor 0%, currentColor 40%, rgba(255, 255, 255, 0.9) 50%, currentColor 60%, currentColor 100%);
+  background-size: 200% 100%;
+  -webkit-background-clip: text;
+  background-clip: text;
+  -webkit-text-fill-color: transparent;
+  animation: sweep-shine 4s linear infinite;
+}
+
+.dark .shine-text {
+  background: linear-gradient(90deg, currentColor 0%, currentColor 40%, #facc15 50%, currentColor 60%, currentColor 100%);
+  background-size: 200% 100%;
+  -webkit-background-clip: text;
+  background-clip: text;
+  -webkit-text-fill-color: transparent;
 }