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/store/invitations.ts

@@ -0,0 +1,21 @@
+import { accountApi, type AccountInvitation } from '@/core-bridge/account';
+import { errorMessage } from '@/core-bridge/errors';
+import { channelPath, navigate } from '@/app/navigation';
+import { useChannels } from './channels';
+import { useToast } from './toast';
+
+export function invitationLabel(row: AccountInvitation): string {
+  return row.channelName || `空间 ${row.channel_id.slice(0, 8)}…`;
+}
+
+/** 接受邀请并进入空间;结果用 toast 反馈,不抛出 */
+export async function acceptInvitation(row: AccountInvitation): Promise<void> {
+  try {
+    await accountApi.acceptInvitation(row.channel_id);
+    await useChannels.getState().refresh();
+    useToast.getState().push({ kind: 'ok', text: `已加入 ${invitationLabel(row)}` });
+    navigate(channelPath(row.channel_id));
+  } catch (cause) {
+    useToast.getState().push({ kind: 'error', text: `加入失败：${errorMessage(cause)}` });
+  }
+}