feat: mail service

gateway/internal/restapi/public_auth.go

@@ -55,6 +55,11 @@ type SendEmailCodeInput struct {
 	// Email is the single client e-mail address that should receive the login
 	// code challenge.
 	Email string `json:"email"`
+
+	// PreferredLanguage stores the canonical BCP 47 language tag derived from
+	// the public Accept-Language header for upstream auth-mail localization and
+	// create-only user registration context.
+	PreferredLanguage string `json:"-"`
 }
 
 // SendEmailCodeResult describes the public REST and adapter payload returned
@@ -204,6 +209,7 @@ func handleSendEmailCode(authService AuthServiceClient, timeout time.Duration) g
 			abortInvalidRequest(c, err.Error())
 			return
 		}
+		input.PreferredLanguage = resolvePreferredLanguage(c.Request.Header.Get("Accept-Language"))
 
 		callCtx, cancel := context.WithTimeout(c.Request.Context(), timeout)
 		defer cancel()