feat: prevent join requests with equal mail

priv/repo/migrations/20260313120000_add_reviewed_by_display_to_join_requests.exs

@@ -0,0 +1,30 @@
+defmodule Mv.Repo.Migrations.AddReviewedByDisplayToJoinRequests do
+  @moduledoc """
+  Adds reviewed_by_display to join_requests for showing reviewer in UI without loading User.
+
+  Backfills existing rows from users.email where reviewed_by_user_id is set.
+  """
+
+  use Ecto.Migration
+
+  def up do
+    alter table(:join_requests) do
+      add :reviewed_by_display, :text
+    end
+
+    # Backfill from users.email for rows that have reviewed_by_user_id
+    execute """
+    UPDATE join_requests j
+    SET reviewed_by_display = u.email
+    FROM users u
+    WHERE j.reviewed_by_user_id = u.id
+      AND j.reviewed_by_user_id IS NOT NULL
+    """
+  end
+
+  def down do
+    alter table(:join_requests) do
+      remove :reviewed_by_display
+    end
+  end
+end