feat: 强化用量计费状态机，新增钱包每日消费汇总分类账

- 将 usage.billing_status 默认值从 settled 改为 pending，完善
  pending -> settled/void 的状态转换逻辑，确保终态不可逆
- 新增 WalletDailyUsageLedger 模型和聚合服务，按账单日汇总
  每个钱包的消费金额、请求数和 token 用量
- 前端钱包中心页面集成每日消费流水展示，支持与充值记录混合
  排序和分页
- 新增两个数据库迁移：修复历史数据状态一致性、创建每日汇总表
- 补充计费状态机单元测试

Closes #218

Co-authored-by: LewisPen <LewisPen@nyadoo.com>

frontend/src/utils/walletDisplay.ts

@@ -35,6 +35,21 @@ export function walletTransactionCategoryLabel(category: string | null | undefin
   return labels[category] || category
 }
 
+export function dailyUsageCategoryLabel(isToday = false): string {
+  return isToday ? '今日消费' : '每日消费'
+}
+
+export function formatTokenCount(value: number | null | undefined): string {
+  const amount = Number(value ?? 0)
+  if (amount >= 1_000_000) {
+    return `${(amount / 1_000_000).toFixed(amount >= 10_000_000 ? 0 : 1)}M`
+  }
+  if (amount >= 1_000) {
+    return `${(amount / 1_000).toFixed(amount >= 10_000 ? 0 : 1)}K`
+  }
+  return `${Math.round(amount)}`
+}
+
 export function walletTransactionReasonLabel(reasonCode: string | null | undefined): string {
   const labels: Record<string, string> = {
     topup_admin_manual: '人工充值',