Start v0.4.0 development - #29

Summary

• advance development from the immutable v0.3.0 release to 0.4.0.dev0
• restore main-pinned links in the generated PyPI description
• record the verified OIDC run, public hashes, attestations, GitHub Release and independent clean install
• preserve all frozen RecoveryBench and calculator artifacts

Public v0.3.0 evidence

• release workflow: https://github.com/DaoyuanLi2816/mini-verl/actions/runs/30772772078
• wheel: e42404ced88b75ba4ff31541cb3df697da0eee09a68f603e4eadbf69a11d2032
• sdist: 006ce418243286dd27e0731090bf9fa1711a1abc962ecfcc4d39807257539cb2
• no-cache Python 3.10 public install reported 0.3.0, passed JSON doctor, and kept the optional ML stack absent

Validation

• PyPI description byte check and Markdown links
• Ruff check/format and mypy src/miniverl
• 86 focused packaging/version tests
• legacy calculator and primary RecoveryBench hashes unchanged

No runtime or scientific result changes.