feat(web): redesign account settings and the sign-in page

- account settings: sidebar sections (profile, devices, security,
  invitations, sync and sign-in) instead of one long scroll; inline device
  rename, confirmations for destructive actions and toast feedback
- sign-in/register: split layout with a quiet brand column, text tabs and
  underlined inputs; registering asks for the password twice and explains
  that it cannot be recovered
- move invitation accept/label helpers into store/invitations so the
  toast and the settings inbox share them
- add the home page zone styles used by the next commit

web/src/features/home/SyncSettings.tsx

@@ -0,0 +1,43 @@
+import { navigate } from '@/app/navigation';
+import { errorMessage } from '@/core-bridge/errors';
+import { useAccount } from '@/store/account';
+import { useToast } from '@/store/toast';
+import { Button } from '@/ui/Button';
+import styles from './AccountSettings.module.css';
+
+export function SyncSettings() {
+  const busy = useAccount((s) => s.busy);
+  const remembered = useAccount((s) => s.remembered);
+  const sync = useAccount((s) => s.sync);
+  const logout = useAccount((s) => s.logout);
+  const clearSavedLogin = useAccount((s) => s.clearSavedLogin);
+  const toast = useToast.getState().push;
+
+  async function syncNow() {
+    try { await sync(); toast({ kind: 'ok', text: '资源保险库已同步' }); }
+    catch (cause) { toast({ kind: 'error', text: `同步失败：${errorMessage(cause)}` }); }
+  }
+  async function clearSaved() {
+    if (!window.confirm('清除本机保存的账号和密码？当前页面仍可使用，刷新后需要重新登录。')) return;
+    try { await clearSavedLogin(); toast({ kind: 'ok', text: '已清除本机保存的登录信息' }); }
+    catch (cause) { toast({ kind: 'error', text: errorMessage(cause) }); }
+  }
+  async function signOut() {
+    if (!window.confirm('退出登录？')) return;
+    await logout();
+    navigate('/');
+  }
+
+  return <section className={styles.page} aria-label="同步与登录">
+    <h2>同步与登录</h2>
+    <div className={styles.group}>
+      <div className={styles.groupText}><strong>资源保险库</strong><small>空间与分享的访问凭据在本机加密后同步，换设备登录即可恢复。</small></div>
+      <Button disabled={busy} onClick={() => { void syncNow(); }}>{busy ? '同步中…' : '立即同步'}</Button>
+    </div>
+    <div className={styles.group}>
+      <div className={styles.groupText}><strong>本机记住登录</strong><small>{remembered ? '已开启：刷新页面后自动恢复登录。只在自己的设备上使用。' : '未开启：刷新或关闭页面后需要重新登录。'}</small></div>
+      {remembered ? <Button disabled={busy} onClick={() => { void clearSaved(); }}>清除本机保存</Button> : null}
+    </div>
+    <div className={styles.footer}><Button className={styles.danger} variant="ghost" disabled={busy} onClick={() => { void signOut(); }}>退出登录</Button></div>
+  </section>;
+}