docs: strengthen final CodeLeWM paper

[AbdelStark]

Summary

• rewrite the final paper around research questions, claim discipline, lessons, and future gates
• add a PGFPlots downstream replay figure directly from the committed v1.0 evidence
• update the paper claim audit and paper-package tests to lock the conservative claim boundary
• rebuild the final PDF and arXiv source bundle

Validation

• scripts/build-codelewm-final-paper
• uv run pytest tests/docs -q
• uv run python -m compileall -q -x 'tests/fixtures/codestate/invalid_(before|after)\.py$' codelewm tests\n- uv run codelewm secret-scan docs/papers/codelewm_final_paper.tex docs/papers/codelewm_final_claim_audit.md docs/papers/codelewm_final_paper.pdf docs/papers/codelewm_final_arxiv_source.tar.gz tests/docs/test_final_paper_package.py --include-suffix .tex --include-suffix .md --include-suffix .pdf --include-suffix .gz --include-suffix .py --json\n- git diff --check\n- verified all existing arXiv eprint URLs in docs/papers/two_substrate_references.bib returned HTTP 200\n