feat(web): 前端共享基础(focusRing/proseBody/text-2xs + useBodyScrollLock + Toast撤销 + error/not-found/loading路由边界)

apps/web/app/loading.tsx

@@ -0,0 +1,9 @@
+import { ThinkingIndicator } from "@/components/ThinkingIndicator";
+
+export default function Loading() {
+  return (
+    <main className="flex min-h-screen items-center justify-center bg-bg px-6 py-16">
+      <ThinkingIndicator label="加载中…" className="text-ink-soft" />
+    </main>
+  );
+}