collatz: extend paliers to 2^24, hensel shifted, phase reports and analyses
**Motivations:**
- Extend terminal and minorated clauses to paliers 2^19–2^24.
- Add hensel chain leaves shifted variant and refinement bundles mod2p21/mod2p24.
- Document grammar extension phases, y_mod3 and prefix diversity analyses.
**Root causes:**
- N/A (evolutions)
**Correctifs:**
- N/A
**Evolutions:**
- Add collatz_analyze_prefix_diversity.py, collatz_analyze_y_mod3_distribution.py.
- Add collatz_build_hensel_chain_leaves_shifted.py, collatz_extract_residues_from_clauses_json.py.
- Extend terminal_clauses_over_Sm and minorated_clauses_over_Sm to palier2p19–2p24.
- Add refinement bundles bundle_mod2p15_to2p21, bundle_mod2p15_to2p24, hensel_shifted variant.
- Add phase reports (option_a_extension_m24, grammar_extensions, y_mod3, prefix_diversity, clause_D_partielle).
- Update README and feature docs.
**Pages affectées:**
- applications/collatz/collatz_k_scripts/README.md
- applications/collatz/collatz_k_scripts/*.py
- docs/artefacts/collatz/**
- docs/features/*.md
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