refactor: 简化 trial 赠送配置，删除多余的白名单启用开关

**简化方案**:
- 删除 `EnableTrialEmailWhitelist` 配置字段（多余）
- 保留 `TrialEmailDomainWhitelist`（逗号分隔的白名单域名）
- 赠送规则：白名单**非空** 且 **邮箱在列表** 才赠送

**新的赠送逻辑**:
```yaml
TrialEmailDomainWhitelist: "qq.com,163.com,gmail.com"
```
- 为空 → ❌ 不赠送（关闭）
- 非空 → ✅ 赠送给白名单域名的邮箱

**更新的地方**:
1. internal/config/config.go - 删除 EnableTrialEmailWhitelist 字段
2. userRegisterLogic.go - 简化赠送逻辑
3. emailLoginLogic.go - 简化赠送逻辑
4. bindEmailWithVerificationLogic.go - 简化赠送逻辑
5. oAuthLoginGetTokenLogic.go - 简化赠送逻辑

**配置升级说明**:
旧配置:
```yaml
EnableTrial: true
EnableTrialEmailWhitelist: true
TrialEmailDomainWhitelist: "qq.com,163.com"
```

新配置（只保留两项）:
```yaml
EnableTrial: true
TrialEmailDomainWhitelist: "qq.com,163.com"
```

关闭赠送:
```yaml
EnableTrial: true
TrialEmailDomainWhitelist: ""
```

Co-Authored-By: claude-flow <ruv@ruv.net>

internal/config/config.go

@@ -87,12 +87,11 @@ type RegisterConfig struct {
 	TrialSubscribe          int64  `yaml:"TrialSubscribe" default:"0"`
 	TrialTime               int64  `yaml:"TrialTime" default:"0"`
 	TrialTimeUnit           string `yaml:"TrialTimeUnit" default:""`
+	TrialEmailDomainWhitelist string `yaml:"TrialEmailDomainWhitelist" default:""`
 	IpRegisterLimit         int64  `yaml:"IpRegisterLimit" default:"0"`
 	IpRegisterLimitDuration int64  `yaml:"IpRegisterLimitDuration" default:"0"`
 	EnableIpRegisterLimit   bool   `yaml:"EnableIpRegisterLimit" default:"false"`
 	DeviceLimit               int64  `yaml:"DeviceLimit" default:"2"`
-	EnableTrialEmailWhitelist bool   `yaml:"EnableTrialEmailWhitelist" default:"false"`
-	TrialEmailDomainWhitelist string `yaml:"TrialEmailDomainWhitelist" default:""`
 }
 
 type EmailConfig struct {

internal/logic/auth/emailLoginLogic.go

@@ -126,7 +126,7 @@ func (l *EmailLoginLogic) EmailLogin(req *types.EmailLoginRequest) (resp *types.
 				return err
 			}
 			rc := l.svcCtx.Config.Register
-			if rc.EnableTrial && (!rc.EnableTrialEmailWhitelist || IsEmailDomainWhitelisted(req.Email, rc.TrialEmailDomainWhitelist)) {
+			if rc.EnableTrial && rc.TrialEmailDomainWhitelist != "" && IsEmailDomainWhitelisted(req.Email, rc.TrialEmailDomainWhitelist) {
 				if err = l.activeTrial(userInfo.Id); err != nil {
 					return err
 				}

internal/logic/auth/oauth/oAuthLoginGetTokenLogic.go

@@ -395,8 +395,8 @@ func (l *OAuthLoginGetTokenLogic) register(email, avatar, method, openid, reques
 		}
 
 		rc := l.svcCtx.Config.Register
-		// Only activate trial if whitelist is not enabled, or email domain matches whitelist
-		shouldActivateTrial := rc.EnableTrial && (!rc.EnableTrialEmailWhitelist || (email != "" && l.isEmailDomainWhitelisted(email, rc.TrialEmailDomainWhitelist)))
+		// Only activate trial if email domain is in whitelist (whitelist cannot be empty)
+		shouldActivateTrial := rc.EnableTrial && rc.TrialEmailDomainWhitelist != "" && (email != "" && l.isEmailDomainWhitelisted(email, rc.TrialEmailDomainWhitelist))
 
 		if shouldActivateTrial {
 			l.Debugw("activating trial subscription",

internal/logic/auth/userRegisterLogic.go

@@ -148,7 +148,7 @@ func (l *UserRegisterLogic) UserRegister(req *types.UserRegisterRequest) (resp *
 
 	// Activate trial subscription after transaction success (moved outside transaction to reduce lock time)
 	rc := l.svcCtx.Config.Register
-	if rc.EnableTrial && (!rc.EnableTrialEmailWhitelist || IsEmailDomainWhitelisted(req.Email, rc.TrialEmailDomainWhitelist)) {
+	if rc.EnableTrial && rc.TrialEmailDomainWhitelist != "" && IsEmailDomainWhitelisted(req.Email, rc.TrialEmailDomainWhitelist) {
 		trialSubscribe, err = l.activeTrial(userInfo.Id)
 		if err != nil {
 			l.Errorw("Failed to activate trial subscription", logger.Field("error", err.Error()))

internal/logic/public/user/bindEmailWithVerificationLogic.go

@@ -209,13 +209,13 @@ func (l *BindEmailWithVerificationLogic) refreshBindSessionToken(userId int64) (
 }
 
 // tryGrantTrialOnEmailBind grants trial subscription to the email user (family owner)
-// if EnableTrial is on and (if whitelist is enabled, email domain must match).
+// if email domain is in the configured whitelist (or if whitelist is empty, no trial is granted).
 func (l *BindEmailWithVerificationLogic) tryGrantTrialOnEmailBind(ownerUserId int64, email string) {
 	rc := l.svcCtx.Config.Register
-	if !rc.EnableTrial {
+	if !rc.EnableTrial || rc.TrialEmailDomainWhitelist == "" {
 		return
 	}
-	if rc.EnableTrialEmailWhitelist && !auth.IsEmailDomainWhitelisted(email, rc.TrialEmailDomainWhitelist) {
+	if !auth.IsEmailDomainWhitelisted(email, rc.TrialEmailDomainWhitelist) {
 		l.Infow("email domain not in trial whitelist, skip",
 			logger.Field("email", email),
 			logger.Field("owner_user_id", ownerUserId),