feat: 新增交易服务，包含交易的增删改查、列表查询（支持筛选和分页）及按日期分组功能。

src/services/transactionService.ts

@@ -29,7 +29,10 @@ function transformTransaction(apiTransaction: Record<string, unknown>): Transact
     amount: apiTransaction.amount as number,
     type: apiTransaction.type as TransactionType,
     categoryId: (apiTransaction.category_id ?? apiTransaction.categoryId) as number,
+    // Map nested objects if they exist
+    category: apiTransaction.category as import('../types').Category | undefined,
     accountId: (apiTransaction.account_id ?? apiTransaction.accountId) as number,
+    account: apiTransaction.account as import('../types').Account | undefined,
     currency: apiTransaction.currency as CurrencyCode,
     transactionDate: (apiTransaction.transaction_date ?? apiTransaction.transactionDate) as string,
     note: apiTransaction.note as string | undefined,