Declare GLFW GLX runtime metadata

[Sunrisepeak]

Summary

• Declare Linux mcpp.runtime metadata for compat.glfw, including GLX/OpenGL dlopen libraries and host capability tags.
• Document the package/runtime boundary for compat.glfw and host GLX driver requirements.
• Add smoke-script static assertions so the runtime metadata remains visible in package validation.

Test plan

• lua5.4 syntax load check for all pkgs/**/*.lua
• bash -n tests/smoke_compat_imgui_window.sh
• metadata grep for dlopen_libs and opengl.glx.driver
• git diff --check

Notes

• Full install smoke remains a follow-up after the runtime metadata support is available through the released mcpp used by package-index validation.