Create bindings/hud.rs exposing HudContext to Lua scripts: - hud.text(), hud.text_centered() for text drawing - hud.rect(), hud.rect_outline() for rectangles - hud.progress_bar() for progress bars with bg/fill colors - hud.flash() for screen flashes (damage feedback) - hud.screen_size() for screen dimensions Features: - Flexible color format: array {r,g,b,a} or named {r=r,g=g,b=b,a=a} - Alpha defaults to 1.0 when omitted - Progress values clamped to 0.0-1.0 - 19 tests covering all functions and edge cases Currently stub implementation logging debug messages. Real rendering requires engine wiring via lua.set_app_data().