Scrap piles become a third selection category: click to select (actors
win on overlap), box-drag / Ctrl+click multi-select, and the selected-
object panel shows the summed remaining amount, updating live and
dropping piles as they are collected or despawn.
- ScrapSystem: expose per-pile amount via ScrapInfo.
- EntityHitTest: add scrapAtWorldPos and scrapInBox (with tests).
- New header-only ScrapSelectionChangedEvent.
- GameWorldView: scrap selection member, click/box handling with the
building-wins disambiguation, and per-frame pruning of gone piles.
- SelectedBuildingPanel: scrap event, "Scrap: N" label, live total;
scrap and building/entity selections clear each other.
Implements REQ-UI-SCRAP-CLICK-SELECT, REQ-UI-SCRAP-MULTI-SELECT,
REQ-UI-SCRAP-PANEL.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01DZR44tA8sn4dPqDzAVXyps
