feat: harden release quality and offline developer experience

[wu-xiaochen]

What changed

• Repositioned the repository around a clear offline reasoning SDK workflow.
• Added a deterministic offline benchmark and regression coverage.
• Hardened Chroma fallback behavior and public import compatibility.
• Unified package/API version reporting.
• Consolidated CI and fixed release artifact handoff.
• Added contributor and security entrypoints.

Why

The project needed a trustworthy first-run path: a new developer should be able to install, run, verify, and understand Clawra without API keys or external services.

Verification

• pytest -q
• python examples/demo_basic.py
• python examples/benchmark_offline.py
• targeted Ruff and compile checks
• workflow YAML parsing
• python -m build
• python -m twine check dist/*

Notes

This PR intentionally keeps the larger historical lint debt out of scope and scopes CI linting to the maintained public entrypoints and new benchmark surface.