B9: Audio system (miniaudio) #147

Summary

Implement the audio system using miniaudio. Support WAV and MP3 playback with 3D positional audio for weapon fire, explosions, and engine sounds.

Requirements

• miniaudio integration (single-file, public domain)
• WAV playback (BC's primary sound format)
• MP3 playback (BC uses MP3 for music)
• 3D positional audio (sounds attenuate with distance, pan with position)
• Sound categories: weapons, engines, explosions, UI, music
• Volume controls per category
• Asset resolver integration for sound file lookup

Acceptance Criteria

• WAV files play correctly
• 3D positional audio works (sounds pan and attenuate)
• Multiple simultaneous sounds
• Music playback (MP3)
• Volume controls

Blocks: #120