[Fix] Clear review eyes reaction on completion

[samzong]

What's changed?

• Keep the existing successful review +1 reaction on event item completion.
• Remove ClawSweeper-owned eyes reactions from the reviewed issue or pull request after successful completion.
• Add a workflow regression test for the completion reaction cleanup path.

Why

• eyes is the in-progress signal; leaving it after a successful review makes completed PRs look like they are still being reviewed.
• The cleanup filters by ClawSweeper bot logins and issue reaction ids, so user reactions and issue comment reactions are left alone.
• Verification: pnpm run build, pnpm run test:unit, pnpm run format:check, git diff --check, and the pre-ship committed-diff gate passed. pnpm run check was attempted and reached unrelated existing repair git fixture failures with fatal: Not a valid object name origin/main.