fix(frontend): Add localStorage migration logic for userId to id field

Automatically migrate old localStorage format where user object has userId field
to new format with id field. This prevents users from needing to re-login after
the backend API response changed from userId to id.

Changes:
- Added migrate function to Zustand persist config to handle userId → id migration
- Added post-hydration safety check in onRehydrateStorage callback
- Added detailed console.log for debugging migration process

Fixes: User data mismatch after API response format change

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

stores/authStore.ts

@@ -33,12 +33,32 @@ export const useAuthStore = create<AuthState>()(
         user: state.user,
         isAuthenticated: state.isAuthenticated,
       }),
+      // 数据迁移函数：将旧格式的 userId 转换为新格式的 id
+      migrate: (persistedState: any, version: number) => {
+        console.log('[AuthStore] Migrating persisted state', { version, persistedState });
+
+        // 如果存在旧的 userId 字段，迁移到 id
+        if (persistedState?.user?.userId && !persistedState?.user?.id) {
+          console.log('[AuthStore] Migrating userId to id');
+          persistedState.user.id = persistedState.user.userId;
+          delete persistedState.user.userId;
+        }
+
+        return persistedState;
+      },
       onRehydrateStorage: () => (state) => {
         console.log('[AuthStore] Hydration started');
         if (state) {
+          // 额外的安全检查：确保 user 对象有 id 字段
+          if (state.user && (state.user as any).userId && !state.user.id) {
+            console.log('[AuthStore] Post-hydration migration: userId -> id');
+            state.user.id = (state.user as any).userId;
+            delete (state.user as any).userId;
+          }
+
           state.isHydrated = true;
           console.log('[AuthStore] Hydration completed', {
-            user: state.user?.id,
+            userId: state.user?.id,
             isAuthenticated: state.isAuthenticated
           });
         }