fix(auth): disable trial grants on public email flows

internal/logic/auth/trialEmailWhitelist.go

@@ -54,6 +54,14 @@ func ShouldGrantTrialForEmail(register config.RegisterConfig, email string) bool
 	return true
 }
 
+// ShouldAutoGrantTrialOnPublicEmailFlows defines whether browser/email-originated
+// flows may auto-create a trial subscription. The current policy disables trial
+// creation for email registration, email login auto-register, OAuth-with-email,
+// and email binding/verification to avoid abuse through public email channels.
+func ShouldAutoGrantTrialOnPublicEmailFlows(register config.RegisterConfig) bool {
+	return false
+}
+
 // 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.