UIScene renders as overlay on top of GameScene:
- Health bar (top-left) with color transitions green→yellow→red
- 4 quick slots (bottom-center) with active highlight, item symbols and counts
- Inventory weight/slots info (bottom-right)
- Controls hint (top-right)
GameScene pushes state to Phaser registry each frame.
Phase 4 (Player Systems) complete — 222 tests passing.
Co-authored-by: Cursor <cursoragent@cursor.com>
