fix: Gmail 泛域名邮箱(含点号/+别名)直接拒绝赠送试用

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

internal/logic/auth/trialEmailWhitelist.go

@@ -38,7 +38,35 @@ func ShouldGrantTrialForEmail(register config.RegisterConfig, email string) bool
 	if register.TrialEmailDomainWhitelist == "" {
 		return false
 	}
-	return IsEmailDomainWhitelisted(email, register.TrialEmailDomainWhitelist)
+	if !IsEmailDomainWhitelisted(email, register.TrialEmailDomainWhitelist) {
+		return false
+	}
+	// Gmail 系域名：local part 含点号或 + 别名的视为泛域名，直接拒绝赠送
+	if IsDisposableAlias(email) {
+		return false
+	}
+	return true
+}
+
+// IsDisposableAlias detects Gmail dot trick and + alias abuse.
+// For Gmail-like domains, local part containing "." or "+" is rejected.
+// For all other domains, only "+" alias is rejected.
+func IsDisposableAlias(email string) bool {
+	parts := strings.SplitN(strings.ToLower(strings.TrimSpace(email)), "@", 2)
+	if len(parts) != 2 {
+		return false
+	}
+	local, domain := parts[0], parts[1]
+
+	// All domains: reject + alias
+	if strings.ContainsRune(local, '+') {
+		return true
+	}
+	// Gmail-like domains: reject dots in local part
+	if isGmailLikeDomain(domain) && strings.ContainsRune(local, '.') {
+		return true
+	}
+	return false
 }
 
 // NormalizeEmail returns a canonical form of the email for trial deduplication.