Feature/audio ext v1

[Pcothren]

Summary
Implements a first usable version of pl_audio_ext (previously placeholder) and adds a minimal audio
example for runtime validation.

What changed

• Added a backend-agnostic plAudioI v1 API in extensions/pl_audio_ext.h
• Implemented pl_audio_ext in extensions/pl_audio_ext.c using vendored miniaudio
• Added examples/example_basic_audio_0.c (generated chiptune-style tone, no external assets)
• Patched examples/build_win32.bat to build example_basic_audio_0

Audio API (v1)

• initialize / cleanup / update
• create clip from memory / file
• play / stop / stop_all / is_playing
• master and voice volume controls

Implementation notes

• Extension state is stored via plDataRegistryI for reload-safe lifecycle
• Public API is backend-agnostic; backend implementation is internal to pl_audio_ext.c
• Vendored dependency: dependencies/miniaudio/miniaudio.h
• v1 is intentionally minimal (no 3D audio / streaming / DSP yet)

Tested (Windows)

• tests\build_win32.bat
• src\build_win32.bat
• examples\build_win32.bat
• out\pilot_light_c.exe
• out\pilot_light_cpp.exe
• out\pilot_light.exe -a tests_c
• out\pilot_light.exe -a tests_cpp
• out\pilot_light.exe --disable_vt -a example_basic_audio_0