test: add GLFW shader validation helper

[sit-d]

Summary

• Add glfw/check_shaders.py, a small helper that runs glslangValidator over the checked-in GLFW GLSL sources.
• Cover the standalone instanced-cube vertex/fragment shaders plus the diagnostic viewer vertex shader and all diagnostic fragment shaders.
• Ignore Python __pycache__/ directories created by syntax and validation runs.

Verification

• python3 -m py_compile glfw/check_shaders.py
• python3 glfw/check_shaders.py — validated 12 shader files
• git diff --check HEAD~1..HEAD

Notes / Limitations

• This validates GLSL parser syntax only; it does not assemble or run the Windows/GLFW examples.
• The full fasm2/Windows/GLFW build was not run.

[sit-d]

Post-guard ad-hoc verification refresh:

• Fresh verifier: /tmp/hermes-verify-fasm2-shaders-postguard-xy8zsa91.py
• Checked glfw/check_shaders.py still inventories the instanced GLSL pair, diagnostic viewer vertex shader, and diagnostic *.frag files.
• Ran python3 glfw/check_shaders.py; it exited 0 and reported validated 12 shader files.
• Created a temporary glfw/__pycache__/check_shaders.cpython-311.pyc and confirmed both the directory and file are ignored by .gitignore with git check-ignore --no-index.
• Ran git diff --check HEAD~1..HEAD and confirmed clean git status --short.
• Verifier exited 0 and was removed.

[sit-d]

Second post-guard ad-hoc verification refresh:

• Fresh verifier: /tmp/hermes-verify-fasm2-shaders-guard2-34xadhdt.py
• Checked glfw/check_shaders.py still references glslangValidator, the instanced GLSL pair, diagnostic viewer vertex shader, diagnostic *.frag glob, and the stage-specific validator invocation.
• Ran python3 glfw/check_shaders.py; it exited 0, produced 12 validate ... lines, and reported validated 12 shader files.
• Created a temporary glfw/__pycache__/check_shaders.cpython-311.pyc and confirmed both the directory and file are ignored by .gitignore with git check-ignore --no-index.
• Ran git diff --check HEAD~1..HEAD and confirmed clean git status --short.
• Verifier exited 0 and was removed.