[codex] Add cluster-aware A2 paper polish

[EigenCharlie]

Summary

• Formalize Supplement Proposition A.2 for cluster-aware Hoeffding tightening under explicit cross-cluster independence.
• Synchronize the body QMD and official submission TEX so A.1/A.2 read as the boundary between no-structure Markov and structure-dependent tightening.
• Make Figures 13 and 14 grayscale-safe through redundant line/marker encodings, a grayscale heatmap, dynamic text contrast, and regenerated PNG/PDF artifacts.
• Capitalize the reproducibility cleanup by noting the YAML/Parquet champion feature contract and update the refactor plan with the completed paper-polish work.

Validation

• just paper-submission
• just lint
• just type-check
• just smoke
• just validate-champion
• just drift-gate
• uv run pytest tests/test_publication_targets.py tests/test_supplement_table_sync.py tests/test_configs/test_lineage_consistency.py -q
• just dvc-status
• grayscale previews inspected for Figures 13/14

No freeze/submission work was performed. No protected champion, conformal, portfolio, HPO, or search stage was rerun.