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/components/admin/admin-antd-registry.tsx

@@ -0,0 +1,39 @@
+"use client";
+
+import { StyleProvider, createCache, extractStyle } from "@ant-design/cssinjs";
+import { unstableSetRender } from "antd";
+import { useServerInsertedHTML } from "next/navigation";
+import { useState, type ReactNode } from "react";
+import { createRoot, type Root } from "react-dom/client";
+
+type ReactRootContainer = (Element | DocumentFragment) & { _reactRoot?: Root };
+
+unstableSetRender((node, container) => {
+  const target = container as ReactRootContainer;
+  target._reactRoot ??= createRoot(target);
+  const root = target._reactRoot;
+  root.render(node);
+  return async () => {
+    await new Promise((resolve) => {
+      setTimeout(resolve, 0);
+    });
+    root.unmount();
+  };
+});
+
+export function AdminAntdRegistry({ children }: { children: ReactNode }) {
+  const [cache] = useState(() => createCache());
+  useServerInsertedHTML(() => {
+    const styleText = extractStyle(cache, { plain: true, once: true });
+    if (styleText.includes('.data-ant-cssinjs-cache-path{content:"";}')) return null;
+    return (
+      <style
+        id="antd-cssinjs"
+        data-rc-order="prepend"
+        data-rc-priority="-1000"
+        dangerouslySetInnerHTML={{ __html: styleText }}
+      />
+    );
+  });
+  return <StyleProvider cache={cache}>{children}</StyleProvider>;
+}