refactor(messages): delegate comment handling to /receiving-feedback skill

[xmtp-coder-agent]

Resolves #124

Summary

Replaces the verbose, multi-paragraph [INSTRUCTIONS] block inside formatPRCommentMessage and formatIssueCommentMessage (src/actions/messages.ts) with a single line:

Use the /receiving-feedback skill to handle the following comment.

The agent already owns that decision logic via its receiving-feedback skill, so keeping a duplicate copy in the message template forced both copies to be kept in sync. This delegates to the skill and keeps the message format clean.

Changes

• src/actions/messages.ts — simplified [INSTRUCTIONS] block in both formatPRCommentMessage and formatIssueCommentMessage. formatFailedCheckMessage is untouched (out of scope).
• src/actions/messages.test.ts — the two "reacts with 👍 for automated" tests now assert the new single-line directive is present and that the old wording (👍, automated) is gone. Header / delimiter / File: / body-content tests unchanged.
• Public signatures and the surrounding message frame (headers, [INSTRUCTIONS] / [END INSTRUCTIONS] / [COMMENT] / [END COMMENT] delimiters, instructions-before-body ordering) are preserved, so call-sites in src/workflows/steps/comment.ts and comment.test.ts require no changes.

Test plan

• npm run check (typecheck + lint + format + 401 vitest tests) passes
• Reviewer confirms the new directive wording is what you want

Note

Replace detailed comment instructions with /receiving-feedback skill directive in PR and issue messages

Updates formatPRCommentMessage and formatIssueCommentMessage in messages.ts to replace multi-step guidance (including thumbs-up reactions and automated comment handling) with a single directive to use the /receiving-feedback skill. Tests in messages.test.ts are updated to match the new output.

^{Macroscope summarized c2f55a9.}