feat: prevent join requests with equal mail

lib/mv_web/live/join_request_live/helpers.ex

@@ -21,9 +21,24 @@ defmodule MvWeb.JoinRequestLive.Helpers do
   @doc """
   Returns the reviewer display string (e.g. email) for a join request, or nil if none.
 
-  Accepts a join request struct or map with optional :reviewed_by_user (loaded User struct).
+  Prefers the denormalized :reviewed_by_display (set on approve/reject) so the UI
+  works for all roles without loading the User resource. Falls back to
+  :reviewed_by_user when loaded (e.g. admin or legacy data before backfill).
   """
   def reviewer_display(req) when is_map(req) do
+    case Map.get(req, :reviewed_by_display) do
+      s when is_binary(s) ->
+        trimmed = String.trim(s)
+        if trimmed == "", do: reviewer_display_from_user(req), else: trimmed
+
+      _ ->
+        reviewer_display_from_user(req)
+    end
+  end
+
+  def reviewer_display(_), do: nil
+
+  defp reviewer_display_from_user(req) do
     user = Map.get(req, :reviewed_by_user)
 
     case user do
@@ -42,6 +57,4 @@ defmodule MvWeb.JoinRequestLive.Helpers do
         nil
     end
   end
-
-  def reviewer_display(_), do: nil
 end