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/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()))