Docs: align softmax modes and release metadata

[debashishc]

Summary

• fix stale docs references to removed CLAUDE.md
• correct public API wording in DEVELOPMENT.md (forge_cute_py.ops.<op>())
• update README benchmark quick reference with softmax benchmark commands and impl-mode notes
• clarify current release state in CONTRIBUTING.md (v0.1.0-rc1 exists; final v0.1.0 pending)
• add changelog bullets for softmax impl-mode selection and benchmark CLI updates

Scope

• docs-only patch (README.md, DEVELOPMENT.md, ROADMAP.md, CHANGELOG.md, CONTRIBUTING.md)
• no runtime code changes

Notes

• follow-up to Add softmax impl mode switch and benchmark/test wiring #39