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/utils/generationNotifier.ts

@@ -0,0 +1,50 @@
+/**
+ * Browser notification + in-app toast for generation task completions.
+ * Falls back gracefully when Notification API is unavailable.
+ */
+
+let permissionGranted = false;
+
+async function requestPermission(): Promise<boolean> {
+  if (permissionGranted) return true;
+  if (typeof Notification === "undefined") return false;
+  if (Notification.permission === "granted") { permissionGranted = true; return true; }
+  if (Notification.permission === "denied") return false;
+  try {
+    const result = await Notification.requestPermission();
+    permissionGranted = result === "granted";
+    return permissionGranted;
+  } catch {
+    return false;
+  }
+}
+
+export function notifyTaskCompleted(label: string, mode: "image" | "video" = "image") {
+  const emoji = mode === "video" ? "🎬" : "🖼️";
+  const title = `${emoji} ${label}生成完成`;
+  const body = "点击返回查看生成结果";
+
+  // Browser notification (background tab)
+  if (typeof Notification !== "undefined" && Notification.permission === "granted") {
+    try { new Notification(title, { body, icon: "/favicon.ico", tag: "gen-complete" }); } catch { /* */ }
+  }
+
+  // In-app toast
+  dispatchGenToast(title);
+}
+
+// Use the existing toast system for in-app notifications
+function dispatchGenToast(msg: string) {
+  try {
+    import("../components/toast/toastStore").then((m) => m.toast(msg, "success"));
+  } catch { /* toast system not loaded */ }
+}
+
+/** Call once on app init to pre-warm permission. */
+export async function initNotificationPermission() {
+  if (typeof Notification === "undefined") return;
+  if (Notification.permission === "default") {
+    // Don't prompt immediately — wait for first user interaction
+    document.addEventListener("click", () => requestPermission(), { once: true });
+  }
+}