docs: add v0.0.3 release criteria

[lsr-05]

Summary

• Add a standalone v0.0.3 milestone close-out checklist.
• Document CPU validation expectations and diagnostics/docs checks.
• Provide explicit language for GPU checks skipped on CPU-only hosts.
• Link the checklist from the documentation navigation.

Validation

• python -m sphinx -b html -D html_theme=alabaster docs %TEMP%/areno-docs-build-issue69

The default shibuya theme is not installed in the validation environment, so the docs were built with alabaster.

Closes #69

[lsr-05]

#69