feat: 实现注册优惠码功能

- 支持创建/编辑/删除优惠码，设置赠送金额和使用限制
  - 注册页面实时验证优惠码并显示赠送金额
  - 支持 URL 参数自动填充 (?promo=CODE)
  - 添加优惠码验证接口速率限制
  - 使用数据库行锁防止并发超限
  - 新增后台优惠码管理页面，支持复制注册链接

backend/internal/handler/admin/promo_handler.go

@@ -27,11 +27,11 @@ func NewPromoHandler(promoService *service.PromoService) *PromoHandler {
 
 // CreatePromoCodeRequest represents create promo code request
 type CreatePromoCodeRequest struct {
-	Code        string  `json:"code"`                                    // 可选，为空则自动生成
-	BonusAmount float64 `json:"bonus_amount" binding:"required,min=0"`   // 赠送余额
-	MaxUses     int     `json:"max_uses" binding:"min=0"`                // 最大使用次数，0=无限
-	ExpiresAt   *int64  `json:"expires_at"`                              // 过期时间戳（秒）
-	Notes       string  `json:"notes"`                                   // 备注
+	Code        string  `json:"code"`                                  // 可选，为空则自动生成
+	BonusAmount float64 `json:"bonus_amount" binding:"required,min=0"` // 赠送余额
+	MaxUses     int     `json:"max_uses" binding:"min=0"`              // 最大使用次数，0=无限
+	ExpiresAt   *int64  `json:"expires_at"`                            // 过期时间戳（秒）
+	Notes       string  `json:"notes"`                                 // 备注
 }
 
 // UpdatePromoCodeRequest represents update promo code request

backend/internal/server/api_contract_test.go

@@ -398,7 +398,7 @@ func newContractDeps(t *testing.T) *contractDeps {
 	settingRepo := newStubSettingRepo()
 	settingService := service.NewSettingService(settingRepo, cfg)
 
-	authHandler := handler.NewAuthHandler(cfg, nil, userService, settingService)
+	authHandler := handler.NewAuthHandler(cfg, nil, userService, settingService, nil)
 	apiKeyHandler := handler.NewAPIKeyHandler(apiKeyService)
 	usageHandler := handler.NewUsageHandler(usageService, apiKeyService)
 	adminSettingHandler := adminhandler.NewSettingHandler(settingService, nil, nil)

backend/internal/service/auth_service_register_test.go

@@ -100,6 +100,7 @@ func newAuthService(repo *userRepoStub, settings map[string]string, emailCache E
 		emailService,
 		nil,
 		nil,
+		nil, // promoService
 	)
 }
 
@@ -131,7 +132,7 @@ func TestAuthService_Register_EmailVerifyEnabledButServiceNotConfigured(t *testi
 	}, nil)
 
 	// 应返回服务不可用错误，而不是允许绕过验证
-	_, _, err := service.RegisterWithVerification(context.Background(), "user@test.com", "password", "any-code")
+	_, _, err := service.RegisterWithVerification(context.Background(), "user@test.com", "password", "any-code", "")
 	require.ErrorIs(t, err, ErrServiceUnavailable)
 }
 
@@ -143,7 +144,7 @@ func TestAuthService_Register_EmailVerifyRequired(t *testing.T) {
 		SettingKeyEmailVerifyEnabled:  "true",
 	}, cache)
 
-	_, _, err := service.RegisterWithVerification(context.Background(), "user@test.com", "password", "")
+	_, _, err := service.RegisterWithVerification(context.Background(), "user@test.com", "password", "", "")
 	require.ErrorIs(t, err, ErrEmailVerifyRequired)
 }
 
@@ -157,7 +158,7 @@ func TestAuthService_Register_EmailVerifyInvalid(t *testing.T) {
 		SettingKeyEmailVerifyEnabled:  "true",
 	}, cache)
 
-	_, _, err := service.RegisterWithVerification(context.Background(), "user@test.com", "password", "wrong")
+	_, _, err := service.RegisterWithVerification(context.Background(), "user@test.com", "password", "wrong", "")
 	require.ErrorIs(t, err, ErrInvalidVerifyCode)
 	require.ErrorContains(t, err, "verify code")
 }