- keyframeGetValue now returns the last keyframe's value for times at or
beyond it, fixes a missing util/math.h include, and asserts keyframes are
sorted by time; adds test/animation/test_keyframe.c
- Adds mainmenu scene/UI and a battle HUD UI frame
- Adds save autosave-related fields and battle scene tweaks
- Adds headless test coverage for cutscenes, entities, and map areas
