feat: 新增账户服务层，实现账户的增删改查及转账功能，并初始化AI记账、交易服务和预算仓库。

internal/service/account_service.go

@@ -12,12 +12,12 @@ import (
 
 // Service layer errors
 var (
-	ErrAccountNotFound           = errors.New("account not found")
-	ErrAccountInUse              = errors.New("account is in use and cannot be deleted")
-	ErrInsufficientBalance       = errors.New("insufficient balance for this operation")
-	ErrSameAccountTransfer       = errors.New("cannot transfer to the same account")
-	ErrInvalidTransferAmount     = errors.New("transfer amount must be positive")
-	ErrNegativeBalanceNotAllowed = errors.New("negative balance not allowed for non-credit accounts")
+	ErrAccountNotFound           = errors.New("账户不存在")
+	ErrAccountInUse              = errors.New("账户正在使用中，无法删除")
+	ErrInsufficientBalance       = errors.New("余额不足")
+	ErrSameAccountTransfer       = errors.New("不能转账给同一个账户")
+	ErrInvalidTransferAmount     = errors.New("转账金额必须大于0")
+	ErrNegativeBalanceNotAllowed = errors.New("非信用账户不允许负余额")
 )
 
 // AccountInput represents the input data for creating or updating an account