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/api/wallet.ts

@@ -60,6 +60,36 @@ export interface WalletTransactionsResponse extends WalletBalanceResponse {
   offset: number
 }
 
+export interface DailyUsageRecord {
+  id?: string | null
+  date: string | null
+  timezone?: string | null
+  total_cost: number
+  total_requests: number
+  input_tokens: number
+  output_tokens: number
+  cache_creation_tokens: number
+  cache_read_tokens: number
+  first_finalized_at?: string | null
+  last_finalized_at?: string | null
+  aggregated_at?: string | null
+  is_today: boolean
+}
+
+export type FlowItem =
+  | { type: 'transaction'; data: WalletTransaction }
+  | { type: 'daily_usage'; data: DailyUsageRecord }
+
+export interface WalletFlowResponse extends WalletBalanceResponse {
+  today_entry: DailyUsageRecord | null
+  items: FlowItem[]
+  total: number
+  limit: number
+  offset: number
+}
+
+export type TodayCostResponse = DailyUsageRecord
+
 export interface PaymentOrder {
   id: string
   order_no: string
@@ -131,6 +161,16 @@ export const walletApi = {
     return response.data
   },
 
+  async getFlow(params?: { limit?: number; offset?: number }): Promise<WalletFlowResponse> {
+    const response = await apiClient.get<WalletFlowResponse>('/api/wallet/flow', { params })
+    return response.data
+  },
+
+  async getTodayCost(): Promise<TodayCostResponse> {
+    const response = await apiClient.get<TodayCostResponse>('/api/wallet/today-cost')
+    return response.data
+  },
+
   async createRechargeOrder(payload: WalletRechargeCreateRequest): Promise<{
     order: PaymentOrder
     payment_instructions: Record<string, unknown>