🕒 feat(ui): standardize Timelines to left mode and unify time display

- Switch Semi UI Timeline to mode="left" in:
  - web/src/components/layout/NoticeModal.jsx
  - web/src/components/dashboard/AnnouncementsPanel.jsx
- Show both relative and absolute time in the `time` prop (e.g. "3 days ago 2025-02-18 10:30")
- Move auxiliary description to the `extra` prop and remove duplicate rendering from content area
- Keep original `extra` data intact; compute and pass:
  - `time`: absolute time (yyyy-MM-dd HH:mm)
  - `relative`: relative time (e.g., "3 days ago")
- Update data assembly to expose `time` and `relative` without overwriting `extra`:
  - web/src/components/dashboard/index.jsx
- No i18n changes; no linter errors introduced

Why: Aligns Timeline layout across the app and clarifies time context by combining relative and absolute timestamps while preserving auxiliary notes via `extra`.

web/src/components/dashboard/index.jsx

@@ -108,10 +108,18 @@ const Dashboard = () => {
 
   // ========== 数据准备 ==========
   const apiInfoData = statusState?.status?.api_info || [];
-  const announcementData = (statusState?.status?.announcements || []).map(item => ({
-    ...item,
-    time: getRelativeTime(item.publishDate)
-  }));
+  const announcementData = (statusState?.status?.announcements || []).map(item => {
+    const pubDate = item?.publishDate ? new Date(item.publishDate) : null;
+    const absoluteTime = pubDate && !isNaN(pubDate.getTime())
+      ? `${pubDate.getFullYear()}-${String(pubDate.getMonth() + 1).padStart(2, '0')}-${String(pubDate.getDate()).padStart(2, '0')} ${String(pubDate.getHours()).padStart(2, '0')}:${String(pubDate.getMinutes()).padStart(2, '0')}`
+      : (item?.publishDate || '');
+    const relativeTime = getRelativeTime(item.publishDate);
+    return ({
+      ...item,
+      time: absoluteTime,
+      relative: relativeTime
+    });
+  });
   const faqData = statusState?.status?.faq || [];
 
   const uptimeLegendData = Object.entries(UPTIME_STATUS_MAP).map(([status, info]) => ({