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/features/home/WelcomeSplash.tsx

@@ -15,7 +15,7 @@ const prefersReducedMotion = typeof window !== "undefined"
 export default function WelcomeSplash({ onEnter }: WelcomeSplashProps) {
   const canvasRef = useRef<HTMLCanvasElement>(null);
   const rafRef = useRef(0);
-  const [showWelcome, setShowWelcome] = useState(false);
+  const [showWelcome, setShowWelcome] = useState(true);
   const [exiting, setExiting] = useState(false);
 
   const handleEnter = useCallback(() => {