fix: move migrations to correct directory

priv/repo/migrations/20260511000000_rename_rooms_offset_columns.exs

@@ -0,0 +1,8 @@
+defmodule Localiser.Repo.Migrations.RenameRoomsOffsetColumns do
+  use Ecto.Migration
+
+  def change do
+    rename table(:rooms), :offset_x, to: :x
+    rename table(:rooms), :offset_y, to: :y
+  end
+end