[shimwell]

Summary

• Unify JEFF 3.3/4.0 ENDF/NJOY generation under generate_jeff (default 4.0), removing the old release-specific entry point.
• Use checked NEA sources, 20 JEFF 3.3 thermal pairs and 128 pairs from the upstream generator, with ENDF/B photon supplements and individual TENDL-2019 C13/O17 replacements for 3.3.
• Preserve isolated workers, error propagation, checksum-aware caches, output validation and manifest-last publication.
• Keep the README consistent with other generators: add only a JEFF table row, with usage, cache behavior and limitations documented in the script docstring and generate_jeff --help.

Testing scope

• Follow the repository standard: no test-file changes, new test dependencies or new workflow jobs in this PR.
• The existing CLI help check now uses generate_jeff instead of the removed command.
• Expanded orchestration, real-data, URL/checksum and downloader tests are deferred to a follow-up PR. The test-only stream-unzip dependency is removed. No production code changed during this test-scope reduction.

Validation and limits

• Existing offline suite: 228 passed, 1 environment-dependent skip (OpenMC is installed), in 2.91 seconds locally. Registered CLI help passed for both releases, including the relocated guidance. Processing code is unchanged by the documentation update.
• No data-processing runs were added or executed for this revision. Full-library NJOY qualification has not been performed.
• Additional temperature-split PuO2/UO2/Zy4 evaluations remain outside the upstream mapping. IAEA download failures remain errors; replacement archives use ZIP CRC and ENDF target checks because published MD5s are unavailable.

The existing CI boundary and explicitly untested IAEA URL are unchanged. Shared download fixes remain identical to #42. All commits and this PR are attributed to shimwell.