Split the zero-copy EGL backend (linux/zerocopy/egl.rs, 1208 lines) into a
facade + egl/gl.rs (plan §W4 / §3.2). gl.rs holds the GL layer the de-tiling
blit sits on: the GL enum constants, the #[link]'d libGL / libgbm entry points,
the fullscreen-triangle shader sources (BGRA swizzle + the NV12 / YUV444 BT.709
convert passes), and the shader/program compile helpers. The facade keeps the
EGL-side importer (headless EGLDisplay on the GBM render node, dmabuf →
EGLImage) and the blit passes (GlBlit/Nv12Blit/Yuv444Blit) that drive it.
Pure move; no behavior change. Linux clippy --all-targets + fmt green.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
