Add IMGUI HUD overlay showing HP, wave, score, and enemy count. Display centered Game Over panel with final score and restart prompt. Add procedural sine-wave audio clips for shooting (440Hz) and enemy kills (220Hz) via voltex_audio. Player blinks white during invincibility. Press R to restart after game over. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>