feat: 品牌改版 v2 — 跟随霓虹数据流 logo

- logo 矢量化：青→蓝→紫渐变 S 数据流（logo.tsx + favicon.svg，web/admin 共用）
- 全站配色跟随 logo：强调色青瓷绿 → 青蓝（浅 #0284C7 / 暗 #38BDF8），中性色转冷蓝，终端窗深岩蓝底
- 紫色克制使用：仅 logo 与 .text-brand-gradient（Hero 标题"AI Agent 工作台"渐变字）
- 导航/页脚/admin 顶栏/登录页挂载 logo 标记
- 终端窗与代码块的提示符、光标、事件标签同步换色

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

admin/src/components/admin-layout.tsx

@@ -2,6 +2,7 @@ import { Link, Outlet, useNavigate } from 'react-router-dom'
 import { LogOut, Moon, Sun } from 'lucide-react'
 import { logout } from '@/api/auth'
 import { useTheme } from '@/components/theme-provider'
+import { LogoMark } from '@/components/logo'
 
 export function AdminLayout() {
   const navigate = useNavigate()
@@ -11,7 +12,8 @@ export function AdminLayout() {
     <div className="flex min-h-screen flex-col">
       <header className="sticky top-0 z-40 border-b border-hairline bg-ground/85 backdrop-blur">
         <div className="mx-auto flex h-14 max-w-5xl items-center justify-between px-6">
-          <Link to="/" className="font-mono text-[14px] font-semibold">
+          <Link to="/" className="flex items-center gap-2.5 font-mono text-[14px] font-semibold">
+            <LogoMark size={24} />
             sundynix <em className="not-italic text-accent">admin</em>
           </Link>
           <div className="flex items-center gap-3">