fix(ux): surface hidden notices, bound report waits, add root boundaries

Framework-level UX fixes found while auditing staging (BUG-216..220).

- chat: route 44 previously discarded composer notices to sonner with
  dedupe, so recovery, cancel and archive feedback is actually visible
  (BUG-216)
- chat: anchor stream auto-scroll to bottom proximity and add a
  jump-to-latest control, so reading history is no longer interrupted
  on every token (BUG-218)
- reports: replace the silent 120s poll cutoff with an explicit
  timed-out state, an 8m budget, stepped backoff and an elapsed
  counter (BUG-217)
- reports: pause polling while the tab is hidden, via a shared hook
- app: add root error, global-error and not-found boundaries (BUG-219)
- admin: add antd SSR style extraction and the React 19 render adapter,
  and move admin-only css out of the global stylesheet (BUG-220)
- membership: run bootstrap fetches concurrently and pause payment
  polling while hidden
- build: configure optimizePackageImports

Verified on top of 2d370f2e: tsc, eslint, next build, and the related
frontend contract suites.

Co-authored-by: Cursor <cursoragent@cursor.com>

frontend/src/app/error.tsx

@@ -0,0 +1,45 @@
+"use client";
+
+import { useEffect } from "react";
+
+import { TriangleAlert } from "lucide-react";
+import Link from "next/link";
+
+import { Button } from "@/components/ui/button";
+
+export default function RootError({
+  error,
+  reset,
+}: {
+  error: Error & { digest?: string };
+  reset: () => void;
+}) {
+  useEffect(() => {
+    console.error("app root error", error.digest ?? error.message);
+  }, [error]);
+
+  return (
+    <main className="flex min-h-svh flex-col items-center justify-center gap-4 px-6 py-12 text-center">
+      <TriangleAlert aria-hidden="true" className="size-8 text-destructive" />
+      <div className="flex flex-col items-center gap-3" role="alert">
+        <h1 className="text-xl font-semibold text-foreground">页面出错了</h1>
+        <p className="max-w-md text-sm text-muted-foreground">
+          页面渲染时发生异常，已保存的对话不受影响。可以重试，或返回对话首页。
+        </p>
+      </div>
+      {error.digest ? (
+        <p className="max-w-md text-xs text-muted-foreground">
+          错误编号 <code className="font-mono">{error.digest}</code>，反馈问题时请一并提供。
+        </p>
+      ) : null}
+      <div className="mt-2 flex flex-wrap items-center justify-center gap-3">
+        <Button type="button" onClick={() => reset()}>
+          重试
+        </Button>
+        <Button render={<Link href="/" />} nativeButton={false} variant="outline">
+          返回对话
+        </Button>
+      </div>
+    </main>
+  );
+}