Wallet与Withdrawal模块：完成分字段重构

核心改造：
1. Wallet模块DTO层全部改为*Cent int64字段
2. Wallet.Entry结构从Amount float64改为AmountCent int64
3. Repository层applyEntry函数使用整数加减，无需浮点运算
4. Withdrawal模块DTO/Request全部改为*Cent字段
5. 所有wallet.AppendEntries调用点改为AmountCent
6. 提现手续费计算改为分单位

技术细节：
- 删除了roundWalletMoney函数（不再需要）
- toAccountDTO/toLedgerDTO使用*Cent字段
- 最小提现金额：10元=1000分
- 最大提现金额：5000元=500000分
- 编译验证通过 ✅

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

backend/internal/modules/withdrawal/dto.go

@@ -6,22 +6,22 @@ import (
 
 // 用户端 DTO
 type WithdrawalDTO struct {
-	ID           uint64     `json:"id"`
-	WithdrawNo   string     `json:"withdraw_no"`
-	UserID       uint64     `json:"user_id"`
-	Amount       float64    `json:"amount"`
-	Fee          float64    `json:"fee"`
-	ActualAmount float64    `json:"actual_amount"`
-	AccountType  string     `json:"account_type"`
-	AccountName  string     `json:"account_name"`
-	AccountNo    string     `json:"account_no"` // 脱敏
-	BankName     string     `json:"bank_name"`
-	Status       string     `json:"status"`
-	ReviewRemark string     `json:"review_remark"`
-	CreatedAt    time.Time  `json:"created_at"`
-	UpdatedAt    time.Time  `json:"updated_at"`
-	ReviewedAt   *time.Time `json:"reviewed_at"`
-	PaidAt       *time.Time `json:"paid_at"`
+	ID              uint64     `json:"id"`
+	WithdrawNo      string     `json:"withdraw_no"`
+	UserID          uint64     `json:"user_id"`
+	AmountCent      int64      `json:"amount_cent"`
+	FeeCent         int64      `json:"fee_cent"`
+	ActualAmountCent int64     `json:"actual_amount_cent"`
+	AccountType     string     `json:"account_type"`
+	AccountName     string     `json:"account_name"`
+	AccountNo       string     `json:"account_no"` // 脱敏
+	BankName        string     `json:"bank_name"`
+	Status          string     `json:"status"`
+	ReviewRemark    string     `json:"review_remark"`
+	CreatedAt       time.Time  `json:"created_at"`
+	UpdatedAt       time.Time  `json:"updated_at"`
+	ReviewedAt      *time.Time `json:"reviewed_at"`
+	PaidAt          *time.Time `json:"paid_at"`
 }
 
 // 管理员端详细 DTO
@@ -31,9 +31,9 @@ type WithdrawalDetailDTO struct {
 	UserID           uint64     `json:"user_id"`
 	UserNickname     string     `json:"user_nickname"`
 	UserPhone        string     `json:"user_phone"`
-	Amount           float64    `json:"amount"`
-	Fee              float64    `json:"fee"`
-	ActualAmount     float64    `json:"actual_amount"`
+	AmountCent       int64      `json:"amount_cent"`
+	FeeCent          int64      `json:"fee_cent"`
+	ActualAmountCent int64      `json:"actual_amount_cent"`
 	PaymentAccountID *uint64    `json:"payment_account_id"`
 	AccountType      string     `json:"account_type"`
 	AccountName      string     `json:"account_name"`
@@ -56,8 +56,8 @@ type WithdrawalDetailDTO struct {
 }
 
 type CreateWithdrawalRequest struct {
-	PaymentAccountID uint64  `json:"payment_account_id" binding:"required"`
-	Amount           float64 `json:"amount" binding:"required,gt=0"`
+	PaymentAccountID uint64 `json:"payment_account_id" binding:"required"`
+	AmountCent       int64  `json:"amount_cent" binding:"required,gt=0"`
 }
 
 type ReviewWithdrawalRequest struct {