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">

admin/src/components/logo.tsx

@@ -0,0 +1,57 @@
+interface LogoMarkProps {
+  size?: number
+  className?: string
+}
+
+/** 品牌 Logo：霓虹数据流 S（青→蓝→紫），深岩底方形 */
+export function LogoMark({ size = 28, className }: LogoMarkProps) {
+  return (
+    <svg
+      width={size}
+      height={size}
+      viewBox="0 0 64 64"
+      className={className}
+      aria-hidden="true"
+    >
+      <defs>
+        <linearGradient id="logo-g" x1="0" y1="0" x2="1" y2="1">
+          <stop offset="0" stopColor="#34E5E0" />
+          <stop offset="0.5" stopColor="#3B82F6" />
+          <stop offset="1" stopColor="#A855F7" />
+        </linearGradient>
+      </defs>
+      <rect width="64" height="64" rx="14" fill="#0B1117" />
+      <g fill="none" strokeLinecap="round">
+        <path
+          d="M22 15 C41 15 41 31 32 32 C23 33 23 49 42 49"
+          stroke="url(#logo-g)"
+          strokeWidth="9"
+          opacity="0.22"
+        />
+        <path
+          d="M22 15 C41 15 41 31 32 32 C23 33 23 49 42 49"
+          stroke="url(#logo-g)"
+          strokeWidth="6"
+          opacity="0.45"
+        />
+        <path
+          d="M22 15 C41 15 41 31 32 32 C23 33 23 49 42 49"
+          stroke="url(#logo-g)"
+          strokeWidth="3.6"
+        />
+      </g>
+      <g fill="#34E5E0">
+        <circle cx="15" cy="13" r="1.4" />
+        <circle cx="10" cy="17" r="1" />
+        <circle cx="14" cy="20" r="0.8" />
+      </g>
+      <g stroke="#A855F7" strokeWidth="0.9" opacity="0.75">
+        <path d="M42 49 L50 46 M42 49 L53 51 M50 46 L53 51" fill="none" />
+      </g>
+      <g fill="#C084FC">
+        <circle cx="50" cy="46" r="1.5" />
+        <circle cx="53" cy="51" r="1.2" />
+      </g>
+    </svg>
+  )
+}