feat: 错误监控面板、生成通知、社区搜索、任务队列优化

- AdminMonitor: admin用户可见的客户端错误实时监控面板，右下角浮窗
- generationNotifier: 生成完成浏览器通知 + 站内Toast
- CommunityPage: 新增搜索框，标题/描述/标签模糊匹配，防抖300ms
- App.tsx: 全局unhandled error/rejection监听上报
- WorkbenchPage: 任务并发提示改为显示当前任务数
- serverConnection: 后端client-errors路由注册
- WelcomeSplash: 欢迎按钮全程显示

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

src/components/AppShell.tsx

@@ -21,6 +21,7 @@ import type { WebNavItem, WebNotification, WebUsageSummary, WebUserSession, WebV
 import NotificationCenter from "./NotificationCenter";
 import { RechargeModal } from "./RechargeModal/RechargeModal";
 import { AnimatedPanel } from "./AnimatedPanel";
+import AdminMonitor from "./AdminMonitor";
 
 interface AppShellProps {
   activeView: WebViewKey;
@@ -470,6 +471,7 @@ function AppShell({
           <div className="web-shell__page">{children}</div>
         </main>
       </div>
+      {session?.user.role === "admin" ? <AdminMonitor /> : null}
       <RechargeModal open={rechargeOpen} onClose={() => setRechargeOpen(false)} currentBalance={displayedBalanceCents} />
     </div>
   );