feat: audio system with 15 procedurally generated sounds via soundgen
- AudioEngine with rodio (WAV playback, throttling, volume, toggle)
- 15 embedded sounds: jump, shoot, hit, explosion, death, pickup, descend,
powerup, step, lava_bubble, acid_sizzle, water_splash, fire_crackle,
ui_click, goblin_growl
- Sound events: shoot, hit, explosion (fireball), pickup, descend, powerup,
jump, combat hit, ambient material sounds (lava/fire/acid/water)
- M key toggles audio in GPU modes
- Ambient sounds: scans 15-cell radius around player, plays throttled sounds
for nearby lava/fire/acid/water
- AudioEngine gracefully degrades when no audio device available
- All 185 tests + 14 scenarios pass
Emil
9ce45cff4a