Block pasted moveables in flipped rooms

[Copilot]

Pasting a moveable into a flipped room bypassed the existing placement restriction and warning shown by manual item placement. This change routes pasted objects through the same flipped-room validation so moveables are rejected consistently while statics remain allowed.

• Placement validation

  • Added a flipped-room placement guard in EditorActions.PlaceObject(...), the shared path used by object placement and object paste.
  • The guard rejects placement only when the target room is the flipped variant (room.IsAlternate).

• Moveables vs. statics

  • Detects moveable items directly via ItemInstance.
  • Preserves existing behavior for statics by only blocking non-static items.

• Grouped paste handling

  • Handles multi-object pastes by checking ObjectGroup contents.
  • Rejects the whole paste if any pasted object in the group is a moveable.

• User-facing behavior

  • Reuses the existing warning text instead of introducing a second variant:
    • You can't add moveables to a flipped room.

private static bool IsInvalidMoveablePlacement(Room room, ObjectInstance instance)
{
    if (!room.IsAlternate)
        return false;

    if (instance is ObjectGroup group)
        return ObjectGroupContainsMoveable(group);

    return ObjectInstanceIsMoveable(instance);
}