Add harness-starter-kit

[baskduf]

Summary

Adds harness-starter-kit to Developer Productivity Tools.

Checklist

• I have read the contribution guidelines
• The tool is AI-related and useful for developers
• I have added a short, clear description of the tool
• The link is not a duplicate of an existing one
• The title of the link is properly capitalized
• The link follows the Awesome List format
• My change does not include unrelated files or changes

Why is this tool awesome?

harness-starter-kit helps developers make AI coding-agent workflows more reliable by turning repeated instructions into durable repository artifacts: AGENTS.md rules, knowledge stores, feedback loops, and drift checks.

Link

https://github.com/baskduf/harness-starter-kit