docs: Update licensing

[Ruari-Phipps]

Summary

Update licensing page to point to licenses.json. Also include missing MLP license text
Fixes deployment for docs

Motivation

Use licenses.json as the one source of truth, to avoid having to maintain two lists

Changes

• Update main license info, remove table and point to licenses.json
• Remove GNU license text
• Add MLP license text
• Update docs build and deploy steps to point to the correct place

Test strategy

• Added/updated unit tests
• Manual CLI testing (poly <command>)
• Tested against a live Agent Studio project
• N/A (docs, config, or trivial change)

Checklist

• ruff check . and ruff format --check . pass
• pytest passes
• No breaking changes to the poly CLI interface (or migration path documented)
• Commit messages follow conventional commits