添加预算管理功能，重构账单和消息视图，优化路由和组件交互

Web/src/App.vue

@@ -9,11 +9,17 @@
         <van-tabbar-item name="statistics" icon="chart-trending-o" to="/" @click="handleTabClick('/statistics')">
           统计
         </van-tabbar-item>
-        <van-tabbar-item name="balance" icon="balance-list" to="/balance" @click="handleTabClick('/balance')">
-          账单
+        <van-tabbar-item name="budget" icon="bill-o" to="/budget" @click="handleTabClick('/budget')">
+          预算
         </van-tabbar-item>
-        <van-tabbar-item name="message" icon="comment" to="/message" @click="handleTabClick('/message')" :badge="messageStore.unreadCount || null">
-          消息
+        <van-tabbar-item 
+          name="balance" 
+          icon="balance-list" 
+          :to="messageStore.unreadCount > 0 ? '/balance?tab=message' : '/balance'" 
+          @click="handleTabClick('/balance')" 
+          :badge="messageStore.unreadCount || null"
+        >
+          账单
         </van-tabbar-item>
         <van-tabbar-item name="setting" icon="setting" to="/setting">
           设置
@@ -69,7 +75,8 @@ const showTabbar = computed(() => {
     route.path === '/calendar' ||
     route.path === '/message' ||
     route.path === '/setting' ||
-    route.path === '/balance'
+    route.path === '/balance' ||
+    route.path === '/budget'
 })
 
 const active = ref('')
@@ -105,11 +112,12 @@ const setActive = (path) => {
       case '/calendar':
         return 'ccalendar'
       case '/balance':
-        return 'balance'
       case '/message':
-        return 'message'
+        return 'balance'
       case '/setting':
         return 'setting'
+      case '/budget':
+        return 'budget'
       default:
         return 'statistics'
     }