fix: join confirmation mail configuration

lib/membership/membership.ex

@@ -364,7 +364,8 @@ defmodule Mv.Membership do
     - `:actor` - Must be nil for public submit (policy allows only unauthenticated).
 
   ## Returns
-    - `{:ok, request}` - Created JoinRequest in status pending_confirmation
+    - `{:ok, request}` - Created JoinRequest in status pending_confirmation, email sent
+    - `{:error, :email_delivery_failed}` - Request created but confirmation email could not be sent (logged)
     - `{:error, error}` - Validation or authorization error
   """
   def submit_join_request(attrs, opts \\ []) do
@@ -390,8 +391,7 @@ defmodule Mv.Membership do
               "Join confirmation email failed for #{request.email}: #{inspect(reason)}"
             )
 
-            # Request was created; return success so the user sees the confirmation message
-            {:ok, request}
+            {:error, :email_delivery_failed}
         end
 
       error ->