Post agent responses as GitHub comments on issues/PRs

[nev-offload]

Problem

The action currently logs "No issue/PR to post to" — the agent runs successfully but never posts its response back to GitHub.

Expected behavior

When triggered by an issue or PR event, the agent's response should be posted as a comment on that issue/PR.

Implementation notes

• Extract issue/PR number from the GitHub event payload (github.event.issue.number, github.event.pull_request.number)
• After the agent completes, use the GitHub API (via @actions/github or octokit) to post a comment with the response
• Handle different trigger types: issues.opened, issue_comment.created, pull_request.opened, etc.
• Format the response nicely (markdown, collapsible sections for long responses)
• Consider a "thinking" indicator — post an initial comment like "🤔 Working on it..." and edit it when done

Priority

P0 — This is the core value proposition. Without this, the action is useless in practice.