Add marketplace.json

[Dev-iL]

Added a marketplace.json file required for installing the plugin in Claude Code.

Changes

How I tested this

Successfully installed from a local folder using claude plugin marketplace add ./hamilton/

Notes

Checklist

• PR has an informative and human-readable title (this will be pulled into the release notes)
• Changes are limited to a single goal (no scope creep)
• Code passed the pre-commit check & code is left cleaner/nicer than when first encountered.
• Any change in functionality is tested
• New functions are documented (with a description, list of inputs, and expected output)
• Placeholder code is flagged / future TODOs are captured in comments
• Project documentation has been updated if adding/changing functionality.

[Dev-iL]

@skrawcz The file I added was generated by Claude code. Please see if any metadata needs to be changed.