refactor(home): split bootstrap, recovery polling, and shells

Move the home startup sequence and consultation recovery poll into
plain functions, and the error and onboarding screens into components.
Landing rules, the 20s fatal screen, retry, and the chart settings
deep link stay the same.

frontend/src/components/home-bootstrap-error.tsx

@@ -0,0 +1,24 @@
+"use client";
+
+import Link from "next/link";
+
+export function HomeBootstrapError({
+  accountError,
+  onRetry,
+}: {
+  readonly accountError: string;
+  readonly onRetry: () => void;
+}) {
+  return (
+    <main className="app-loading app-loading-error">
+      <div className="app-loading-content" role="alert">
+        <strong>暂时无法进入 Jyotisha</strong>
+        <span>{accountError}</span>
+        <div className="app-loading-actions">
+          <button className="button-primary" type="button" onClick={onRetry}>重试</button>
+          <Link className="button-secondary" href="/login">返回登录</Link>
+        </div>
+      </div>
+    </main>
+  );
+}