feat(angle): add desktop ANGLE runtime builds

[Alx8g]

Summary

• add reproducible ANGLE EGL and OpenGL ES runtime builds pinned to exact ANGLE and depot_tools revisions
• package Linux and macOS x64/arm64 headers and shared libraries
• validate each package with an ANGLE triangle render and pixel readback
• use system Vulkan on Linux and relocatable, ad-hoc-signed dylibs on macOS

Validation

• Linux x64 package test renders through Lavapipe and reads back 255, 0, 0, 255
• MystralNative context, JavaScript bindings, X11 presentation, and full CLI integration pass locally
• pull request CI builds and render-tests Linux x64/arm64 and macOS Intel/Apple Silicon

Supports the desktop ANGLE packaging requested for MystralNative WebGL 2.

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