ci: reduce noise in Claude PR review and label-check prompts

[Troublor]

Summary

• Update PR review prompt to check existing conversation history before posting, avoid duplicating resolved feedback, and calibrate review effort to PR size. Enforces exactly one top-level comment per review.
• Update label-check prompt to manage its own comments: edit existing comment when labels change, delete it when labels are fixed, and avoid posting duplicate comments.
• Add gh api to label-check allowed tools to support comment deletion.

Test plan

• Open a PR and verify the review bot posts at most one top-level comment
• Push a fix to the PR and verify the bot does not re-raise resolved review threads
• Change labels on a PR and verify the label-check bot edits or deletes its prior comment instead of posting a new one