Fix Credo Design (AliasUsage): add aliases in lib

Add module aliases at top and use short names instead of
fully qualified nested modules across lib/.

lib/mv_web/plugs/check_page_permission.ex

@@ -25,6 +25,7 @@ defmodule MvWeb.Plugs.CheckPagePermission do
 
   import Plug.Conn
   import Phoenix.Controller
+  alias Mv.Authorization.Actor
   alias Mv.Authorization.PermissionSets
   require Logger
 
@@ -37,7 +38,7 @@ defmodule MvWeb.Plugs.CheckPagePermission do
       # Ensure role is loaded (load_from_session does not load it; required for permission check)
       user =
         conn.assigns[:current_user]
-        |> Mv.Authorization.Actor.ensure_loaded()
+        |> Actor.ensure_loaded()
 
       conn = Plug.Conn.assign(conn, :current_user, user)
       page_path = get_page_path(conn)