feat: 全站 PageShell 设计系统与专业 UI 统一

- 新增 PageShell/PageTabs/ContentPanel/PageLoading/PageEmpty 页面骨架
- index.css 设计令牌文档化，布局令牌与纯色主按钮（去除渐变粉彩）
- 全站路由页接入 PageShell，云账单三 Tab 为标杆
- 主题体系：跟随系统 + 主流/开发者分组，新增 Dracula/Tokyo Night，One Dark 暖灰差异化
- 登录页/侧栏/顶栏去渐变光球，企业克制风
- 修复 AIAlertAnalyzer JSX 与构建依赖导入问题

frontend/src/components/monitor/dashboard/GrafanaPanelContent.tsx

@@ -147,11 +147,11 @@ export function GrafanaPanelContent({ panel, datasourceUrl }: { panel: Panel; da
       const unit = (panel.options as any)?.unit ?? '';
       return (
         <div className="flex flex-col items-center justify-center h-full min-h-[120px]">
-          <span className="text-4xl font-bold text-blue-500">
+          <span className="text-4xl font-bold dg-text-blue">
             {val > 1000 ? (val / 1000).toFixed(1) + 'K' : val.toFixed(2)}
           </span>
           {unit && <span className="text-sm text-[var(--dg-text-muted)] mt-2">{unit}</span>}
-          <div className="flex items-center gap-1 mt-2 text-green-500 text-sm">
+          <div className="flex items-center gap-1 mt-2 dg-text-green text-sm">
             <TrendingUp className="w-4 h-4" />
             <span>实时</span>
           </div>
@@ -205,7 +205,7 @@ export function GrafanaPanelContent({ panel, datasourceUrl }: { panel: Panel; da
                   {Object.entries(row.labels).slice(0, 3).map(([k, v]) => (
                     <td key={k} className="py-1 px-2 text-[var(--dg-text-secondary)]">{v}</td>
                   ))}
-                  <td className="py-1 px-2 text-right font-mono text-blue-400">{row.value.toFixed(2)}</td>
+                  <td className="py-1 px-2 text-right font-mono dg-text-blue">{row.value.toFixed(2)}</td>
                 </tr>
               ))}
             </tbody>