feat: add standalone account-import route (#frame=account-import)

- Add 'account-import' to AppPage type and productionAppPages
- Create AccountImportPage.tsx with full-page layout (header + two-column + footer)
- Register lazy route in App.tsx; onDone navigates back to accounts
- Add common.back translation (zh: 返回 / en: Back)

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: linhay

frontend/src/App.tsx

@@ -16,6 +16,7 @@ import { useAppNavigation } from './hooks/useAppNavigation';
 import { toErrorMessage } from './utils/error';
 import { hasWailsRuntime } from './utils/previewMode';
 
+const AccountImportPage = lazy(() => import('./pages/AccountImportPage'));
 const AccountsPage = lazy(() => import('./pages/AccountsPage'));
 const ClaudePage = lazy(() => import('./pages/ClaudePage'));
 const CodexPage = lazy(() => import('./pages/CodexPage'));
@@ -142,6 +143,9 @@ function AppShell() {
     if (activePage === 'design-system') {
       return <DesignSystemPage />;
     }
+    if (activePage === 'account-import') {
+      return <AccountImportPage onDone={() => setActivePage('accounts')} />;
+    }
     if (activePage === 'proxy-pool') {
       return <ProxyPoolPage />;
     }

frontend/src/locales/en.json

@@ -22,7 +22,8 @@
     "no": "No",
     "confirm_delete": "Delete this record?",
     "loading": "Loading...",
-    "more_actions": "More Actions"
+    "more_actions": "More Actions",
+    "back": "Back"
   },
   "nav": {
     "status": "STATUS",

frontend/src/locales/zh.json

@@ -22,7 +22,8 @@
     "no": "否",
     "confirm_delete": "确认删除此记录吗？",
     "loading": "数据加载中...",
-    "more_actions": "更多操作"
+    "more_actions": "更多操作",
+    "back": "返回"
   },
   "nav": {
     "status": "运行状态",