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/system/LiveMonitorDialog.tsx

@@ -200,7 +200,7 @@ export function LiveMonitorDialog({ open, onOpenChange, sessionId, sessionInfo }
         {/* 工具栏 — 与 TerminalDialog 一致 // Logan.Li */}
         <div className="flex items-center justify-between px-4 py-2 border-b border-[var(--dg-border)]">
           <div className="flex items-center gap-2 text-sm min-w-0 flex-wrap">
-            <Monitor className="h-4 w-4 text-emerald-400 shrink-0" />
+            <Monitor className="h-4 w-4 dg-text-green shrink-0" />
             <span className="text-[var(--dg-text-primary)] font-medium">终端实时监控</span>
             {meta && (
               <span className="text-[var(--dg-text-muted)] truncate">
@@ -208,18 +208,18 @@ export function LiveMonitorDialog({ open, onOpenChange, sessionId, sessionInfo }
               </span>
             )}
             {connected && (
-              <Badge variant="outline" className="border-emerald-500/30 text-emerald-400 bg-emerald-500/10 text-xs">
+              <Badge variant="outline" className="border-emerald-500/30 dg-text-green bg-emerald-500/10 text-xs">
                 ● 在线
               </Badge>
             )}
             {!connected && !connectError && (
-              <Badge variant="outline" className="border-yellow-500/30 text-yellow-400 bg-yellow-500/10 text-xs">
+              <Badge variant="outline" className="border-yellow-500/30 dg-text-yellow bg-yellow-500/10 text-xs">
                 <Loader2 className="h-3 w-3 animate-spin mr-1" />
                 连接中
               </Badge>
             )}
             {connectError && (
-              <Badge variant="outline" className="border-red-500/30 text-red-400 bg-red-500/10 text-xs">
+              <Badge variant="outline" className="border-red-500/30 dg-text-red bg-red-500/10 text-xs">
                 连接失败
               </Badge>
             )}
@@ -244,7 +244,7 @@ export function LiveMonitorDialog({ open, onOpenChange, sessionId, sessionInfo }
         </div>
 
         {connectError && (
-          <p className="text-sm text-red-400 px-4 py-2 border-b border-[var(--dg-border)]">{connectError}</p>
+          <p className="text-sm dg-text-red px-4 py-2 border-b border-[var(--dg-border)]">{connectError}</p>
         )}
 
         <div