feat: 3D spatial audio and audio asset pipeline

[Hekbas]

Implement an audio system with 3D spatial sound, an audio asset pipeline, and editor integration.

Tasks

• Choose audio backend (miniaudio, FMOD, OpenAL, or SoLoud)
• Integrate audio library as a dependency
• Implement AudioSystem with initialization, update, and shutdown
• Create AudioSource and AudioListener components
• Implement 3D spatial audio (distance attenuation, panning, Doppler)
• Build audio asset pipeline: import WAV/OGG/MP3, generate .luthaudio artifacts
• Add audio source inspector (clip, volume, pitch, loop, spatial blend, min/max distance)
• Implement audio mixer (master, music, SFX channels)
• Editor: audio preview playback in inspector