chore(frontend): 关于页二维码改为 import 本地资源，不再依赖 CDN

之前 about 页直接拉腾讯云 COS 上的 wechat.png，每次换码都要手动重新上传 CDN
+ 刷缓存。改成 import @/assets/wechat.png，由 Vite 打包，更新时只需替换文件。

doc/wechat.png 仍保留作为源 / 备份。

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

BillNote_frontend/src/pages/SettingPage/about.tsx

@@ -5,6 +5,7 @@ import { Tabs, TabsContent, TabsList, TabsTrigger } from '@/components/ui/tabs'
 import { Github, Star, ExternalLink, Download } from 'lucide-react'
 import { ScrollArea } from '@/components/ui/scroll-area.tsx'
 import logo from '@/assets/icon.svg'
+import wechatQr from '@/assets/wechat.png'
 
 export default function AboutPage() {
   const images = [
@@ -204,7 +205,7 @@ export default function AboutPage() {
               <div className="text-center">
                 <h3 className="mb-3 text-xl font-semibold">BiliNote 交流微信群</h3>
                 <div className="bg-muted mx-auto flex h-52 w-52 items-center justify-center rounded-md">
-                  <img src={'https://common-1304618721.cos.ap-chengdu.myqcloud.com/wechat.png'} />
+                  <img src={wechatQr} alt="BiliNote 交流微信群" className="h-full w-full object-contain" />
                 </div>
               </div>
             </div>