Embed Metal shaders for standalone binaries

[kernelzeroday]

Summary

• embed h3_shaders.metal in both the CLI executable and libh3.a
• compile the embedded source when no shader path is supplied, or when the default source-tree path is unavailable
• retain explicit external shader paths for development and diagnostics
• document single-file installation and exercise the embedded path in the Metal primitive test

Why

The high-level runtime passes a relative h3_shaders.metal path. As a result, copying h3 into a bin directory does not produce a usable CLI unless the shader source is copied alongside it or the command happens to run from the repository root.

Embedding the source keeps runtime Metal compilation (including device-specific preprocessor options) while making the executable relocatable and self-contained. It adds only the existing ~201 KiB shader source to linked binaries.

Validation

• make -j16
• make test -j16 — 1,768 core checks plus native AudioVAE Metal primitives and FFmpeg mux test pass
• linked tests/test_audio_gpu.o against libh3.a and ran it from /tmp with no shader resource present
• copied h3 alone to /tmp and completed a real 256x256, 22-frame MiniMax-H3 render from there; ffprobe confirmed H.264 video and 32 kHz stereo AAC output