feat: 品牌标识用云+数据库矢量图标（favicon + 页眉品牌标）

- Icons.jsx 新增 CloudDbIcon：照 icons8-云 重绘为矢量，左云随主题色、右圆柱用品牌蓝
- GlobalHeader 品牌区前置该图标，原「系统在线」绿点改为挂在其右下角
- index.html 增加 rel=icon / mask-icon 指向 public/favicon.svg
- luxury.css 补品牌样式，并让 :not() 选择器排除 .brand-mark 避免样式误伤

frontend/src/components/GlobalHeader.jsx

@@ -1,7 +1,7 @@
 import React, { useEffect, useMemo, useRef, useState } from 'react'
 import { useNavigate } from 'react-router-dom'
 import axios from 'axios'
-import { BotIcon, ClockIcon, PlusCircleIcon, SearchIcon } from './Icons'
+import { BotIcon, ClockIcon, CloudDbIcon, PlusCircleIcon, SearchIcon } from './Icons'
 
 function GlobalHeader({ onOpenAssistant }) {
   const [now, setNow] = useState(new Date())
@@ -49,7 +49,7 @@ function GlobalHeader({ onOpenAssistant }) {
 
   return (
     <header className="global-header">
-      <div className="global-header-brand"><span className="header-status-dot" /><div><strong>happy出口通</strong><span>EXPORT OPERATIONS CONSOLE</span></div></div>
+      <div className="global-header-brand"><span className="brand-mark" title="happy出口通"><CloudDbIcon size={28} /><span className="header-status-dot" /></span><div><strong>happy出口通</strong><span>EXPORT OPERATIONS CONSOLE</span></div></div>
       <div className={`global-search ${searchOpen ? 'is-open' : ''}`}>
         <SearchIcon size={17} />
         <input ref={searchRef} aria-label="搜索 everything" value={query} onFocus={() => setSearchOpen(true)} onChange={event => setQuery(event.target.value)} placeholder="搜索 everything" autoComplete="off" />

frontend/src/components/Icons.jsx

@@ -25,6 +25,23 @@ export const FactoryIcon = ({ size = 20, className = '' }) => (
   </svg>
 )
 
+/* 品牌标识：云 + 数据库圆柱（照 icons8-云 重绘为矢量）
+   左半边云跟随主题色，右半边圆柱固定品牌蓝；坐标用 24 网格，内部 0.48 缩放。 */
+export const CloudDbIcon = ({ size = 20, className = '' }) => (
+  <svg width={size} height={size} viewBox="0 0 24 24" fill="none" strokeLinecap="round" strokeLinejoin="round" className={className} aria-hidden="true">
+    {/* 云：闭合圆头轮廓 */}
+    <g transform="translate(1 6) scale(0.48)" stroke="currentColor" strokeWidth="3.54">
+      <path d="M17.5 19H9a7 7 0 1 1 6.71-9h1.79a4.5 4.5 0 1 1 0 9Z" />
+    </g>
+    {/* 数据库圆柱：顶盖椭圆 + 桶身 + 中间分层线 */}
+    <g transform="translate(12.4 5.4) scale(0.48)" style={{ stroke: 'var(--primary)' }} strokeWidth="3.54">
+      <ellipse cx="12" cy="5.5" rx="8.5" ry="3.2" />
+      <path d="M3.5 5.5V19.5A8.5 3.2 0 0 0 20.5 19.5V5.5" />
+      <path d="M3.5 12.5A8.5 3.2 0 0 0 20.5 12.5" />
+    </g>
+  </svg>
+)
+
 export const DownloadIcon = ({ size = 20, className = '' }) => (
   <svg width={size} height={size} viewBox="0 0 24 24" fill="none" stroke="currentColor" strokeWidth="2" strokeLinecap="round" strokeLinejoin="round" className={className}>
     <path d="M21 15v4a2 2 0 0 1-2 2H5a2 2 0 0 1-2-2v-4" />