Fix: HasPermission auto_filter and strict_check implementation

Fixes security issue where auto_filter returned nil instead of proper
filter expressions, which could lead to incorrect authorization behavior.

test/mv/authorization/checks/has_permission_integration_test.exs

@@ -72,14 +72,15 @@ defmodule Mv.Authorization.Checks.HasPermissionIntegrationTest do
   end
 
   describe "Filter Expression Structure - :all scope" do
-    test "Admin can read all members without filter" do
+    test "Admin can read all members without filter (returns expr(true))" do
       actor = create_actor_with_role("admin")
       authorizer = create_authorizer(Mv.Membership.Member, :read)
 
       filter = HasPermission.auto_filter(actor, authorizer, [])
 
-      # :all scope should return nil (no filter needed)
-      assert is_nil(filter)
+      # :all scope should return [] (empty keyword list = no filter = allow all records)
+      # After auto_filter fix: no longer returns nil, returns [] instead
+      assert filter == []
     end
   end