refactor: 前端本地偏好统一为公共存储层

- 新增 frontend/src/utils/storageKeys.ts 集中维护存储键常量并登记旧键迁移
- 新增 frontend/src/utils/storage.ts 统一 localStorage/sessionStorage 读写与异常容错
- 新增 frontend/src/composables/usePreference.ts 提供 useStringPreference 响应式字符串偏好
- 新增 frontend/src/utils/transactionFilterPrefs.ts 抽出收支筛选偏好字段定义与共享读写
- 存储键统一以 finance. 前缀命名，locale、emailBill.tab、logs.tab 迁移到新键并自动迁移旧值
- 各页面与组件改用公共层，移除重复的 try/catch 与跨组件重复的序列化逻辑
- 认证凭据 token 属登录状态，保持原键名不纳入 finance. 前缀

frontend/src/router/index.ts

@@ -3,6 +3,8 @@ import { createRouter, createWebHistory } from 'vue-router'
 import { useUserStore } from '../store/user'
 import { useDatabaseStore } from '../store/database'
 import { useRegistrationStore } from '../store/registration'
+import { migrateKey, readString } from '../utils/storage'
+import { LEGACY_STORAGE_KEYS, STORAGE_KEYS } from '../utils/storageKeys'
 
 // 创建路由实例，使用 HTML5 History 模式
 const router = createRouter({
@@ -68,7 +70,9 @@ const router = createRouter({
           // 跳转到上次访问的标签页，无记录时默认邮箱配置
           redirect: () => {
             const tabs = ['configs', 'senderRules', 'messages']
-            const saved = typeof localStorage !== 'undefined' ? localStorage.getItem('emailBill.tab') : null
+            // 读取前迁移旧键，保证老用户标签页偏好不丢失
+            migrateKey(LEGACY_STORAGE_KEYS.emailBillTab, STORAGE_KEYS.emailBillTab)
+            const saved = readString(STORAGE_KEYS.emailBillTab) || null
             return `/email-bills/${saved && tabs.includes(saved) ? saved : 'configs'}`
           },
         },
@@ -92,7 +96,9 @@ const router = createRouter({
           // 跳转到上次访问的日志标签页，无记录时默认访问日志
           redirect: () => {
             const tabs = ['http', 'login', 'app']
-            const saved = typeof localStorage !== 'undefined' ? localStorage.getItem('logs.tab') : null
+            // 读取前迁移旧键，保证老用户标签页偏好不丢失
+            migrateKey(LEGACY_STORAGE_KEYS.logsTab, STORAGE_KEYS.logsTab)
+            const saved = readString(STORAGE_KEYS.logsTab) || null
             return `/logs/${saved && tabs.includes(saved) ? saved : 'http'}`
           },
         },