fix: 修复数据库配置和事务一致性问题

数据库配置:
- SQLite 开启 WAL 模式，读写可并发
- 设置 busy_timeout=5000ms 避免锁超时
- 设置 synchronous=NORMAL 平衡性能和安全
- SQLite MaxOpenConns 设为 1 避免并发写入冲突

事务修复:
- auth.go: 注册流程(用户+设备+会话)加入事务
- auth.go: 密码重置(修改密码+标记验证码)加入事务
- cards.go: 卡密使用加入事务，补充 UsedAt 字段
- cards.go: 代理商批量生成(扣款+生成卡密)加入事务
- extension.go: 充值(修改余额+记录)加入事务
- extension.go: 扣费(修改余额+记录)加入事务
- storage_config.go: 设置默认存储加入事务

backend/internal/router/extension/extension.go

@@ -272,7 +272,15 @@ func handleRechargeUser(c *gin.Context) {
 		return
 	}
 
-	if err := database.DB.Save(&user).Error; err != nil {
+	tx := database.DB.Begin()
+	defer func() {
+		if r := recover(); r != nil {
+			tx.Rollback()
+		}
+	}()
+
+	if err := tx.Save(&user).Error; err != nil {
+		tx.Rollback()
 		service.LogVerification(c, &app.ID, &user.ID, "extension_recharge_failed", fmt.Sprintf("扩展API充值失败: 保存失败 - %s", user.Username), "", err)
 		response.Error(c, 500, "充值失败")
 		return
@@ -286,7 +294,13 @@ func handleRechargeUser(c *gin.Context) {
 		PaymentType: "extension_api",
 		Remark:      req.Description,
 	}
-	database.DB.Create(&record)
+	if err := tx.Create(&record).Error; err != nil {
+		tx.Rollback()
+		response.Error(c, 500, "充值失败")
+		return
+	}
+
+	tx.Commit()
 
 	service.LogVerification(c, &app.ID, &user.ID, "extension_recharge", fmt.Sprintf("扩展API充值: 用户%s, 类型:%s, 数量:%d", user.Username, req.Type, req.Amount), "", nil)
 
@@ -355,7 +369,15 @@ func handleDeductUser(c *gin.Context) {
 		return
 	}
 
-	if err := database.DB.Save(&user).Error; err != nil {
+	tx := database.DB.Begin()
+	defer func() {
+		if r := recover(); r != nil {
+			tx.Rollback()
+		}
+	}()
+
+	if err := tx.Save(&user).Error; err != nil {
+		tx.Rollback()
 		service.LogVerification(c, &app.ID, &user.ID, "extension_deduct_failed", fmt.Sprintf("扩展API扣费失败: 保存失败 - %s", user.Username), "", err)
 		response.Error(c, 500, "扣除失败")
 		return
@@ -370,7 +392,13 @@ func handleDeductUser(c *gin.Context) {
 		PaymentType: "extension_api",
 		Remark:      req.Description,
 	}
-	database.DB.Create(&record)
+	if err := tx.Create(&record).Error; err != nil {
+		tx.Rollback()
+		response.Error(c, 500, "扣除失败")
+		return
+	}
+
+	tx.Commit()
 
 	service.LogVerification(c, &app.ID, &user.ID, "extension_deduct", fmt.Sprintf("扩展API扣费: 用户%s, 类型:%s, 数量:%d", user.Username, req.Type, req.Amount), "", nil)