refactor: unified brand naming to BoosChat

Rebrand all user-facing product name references from legacy
Chinese name to unified "BoosChat" across frontend components,
metadata, test fixtures, and documentation.

web/app/dashboard/login/page.tsx

@@ -16,7 +16,7 @@ export default function LoginPage() {
             </div>
             <div className="space-y-3">
               <h2 className="max-w-lg text-5xl font-semibold tracking-tight">
-                贝壳AI客服
+                BoosChat
               </h2>
               <p className="max-w-xl text-sm leading-6 text-white/72">
                 懂问题，更懂用户；快响应，更能落地。
@@ -50,12 +50,12 @@ export default function LoginPage() {
           <Link href="/dashboard/login" className="flex items-center gap-2 font-medium">
             <img
               src="/images/logo.svg"
-              alt="CS Agent"
+              alt="BoosChat"
               width="32"
               height="32"
               className="size-7 shrink-0 object-contain"
             />
-            CS Agent
+            BoosChat
           </Link>
         </div>
         <div className="flex flex-1 items-center justify-center">

web/app/layout.tsx

@@ -23,8 +23,8 @@ const geistMono = Geist_Mono({
 })
 
 export const metadata: Metadata = {
-  title: "AI 客服后台管理系统",
-  description: "AI 客服后台管理系统",
+  title: "BoosChat",
+  description: "BoosChat 智能客服系统",
 }
 
 export default function RootLayout({