Rename npm package to patchmill

[rochecompaan]

Summary

• Rename the canonical npm package from @rochecompaan/patchmill to patchmill.
• Update Release Please metadata and README install/npx migration guidance.
• Update the release config test expectation for the new package name.

Test Plan

• npm run lint:md
• npm run build
• npm test
• npm pack --dry-run

Post-release follow-up

After the first successful patchmill publish, deprecate the old scoped package:

npm deprecate "@rochecompaan/patchmill@*" "Package renamed to patchmill. Install with: npm install -g patchmill or use: npx patchmill"