Improve OpenHands PR comment feedback

[rickylabs]

Summary

Improves the OpenHands workflow comment lifecycle after the first successful PLAN-EVAL trigger on PR #19.

Changes

• Adds an immediate eyes reaction to trusted @openhands-agent trigger comments.
• Posts one running status comment with model/provider/output mode and the Actions run URL.
• Edits that same status comment with the final summary instead of creating a second final comment.
• Tightens the OpenHands prompt and repo context so agents write .llm/tmp/openhands/summary.md and do not post GitHub comments directly.
• Documents the single-comment lifecycle in AGENTS-handoff.md, .openhands/microagents/repo.md, and the openhands-handoff skill.

Validation

• deno fmt --check .github/workflows/openhands-agent.yml AGENTS-handoff.md .openhands/microagents/repo.md .agents/skills/openhands-handoff/SKILL.md PASS.
• deno eval --no-lock "import { parse } from 'jsr:@std/yaml'; parse(await Deno.readTextFile('.github/workflows/openhands-agent.yml'));" PASS.

Deno still emits the pre-existing examples/playground/deno.json workspace warnings; unrelated to this PR.