Add update_pull_request_comment and delete_pull_request_comment tools

Bắt đầu bằng cách xác định công cụ add_reply_to_pull_request_comment hiện có và mẫu yêu cầu API GitHub của công cụ đó. Thêm các công cụ cập nhật và xóa tương ứng bằng cách sử dụng các endpoint REST và tham số đã nêu, sau đó xác minh rằng mỗi công cụ đều nhắm đến bình luận của người dùng đã xác thực như mô tả và hỗ trợ body được yêu cầu cho việc cập nhật.

Describe the feature or problem you'd like to solve

The MCP server provides add_reply_to_pull_request_comment for PR review comments, but there is no way to edit or delete an existing review comment. The only available mutation is adding a new reply underneath an existing comment.

When an agent needs to correct or retract a review comment it previously posted, the current workaround is to post a new reply — leaving the stale original visible and creating thread noise. The alternative is falling back to gh api with PATCH/DELETE on /repos/{owner}/{repo}/pulls/comments/{id}, bypassing the MCP server entirely.

Proposed solution

Add two new tools that map to the existing GitHub REST API endpoints:

update_pull_request_comment

• REST API: PATCH /repos/{owner}/{repo}/pulls/comments/{comment_id}
• Parameters: owner, repo, comment_id (number), body (string — new body text)
• Auth constraint: Can only update comments authored by the authenticated user
• Equivalent gh command: gh api repos/{owner}/{repo}/pulls/comments/{id} -X PATCH -f body="..."

delete_pull_request_comment

• REST API: DELETE /repos/{owner}/{repo}/pulls/comments/{comment_id}
• Parameters: owner, repo, comment_id (number)
• Auth constraint: Can only delete comments authored by the authenticated user
• Equivalent gh command: gh api repos/{owner}/{repo}/pulls/comments/{id} -X DELETE

Both endpoints are already documented in the GitHub REST API and require no new upstream features.

Additional context

This gap caused a real-world problem: an agent posted review replies that should have been edits to the original comments. The discussion_r{N} URL identifier ≠ the API comment id (a separate but related confusion — see #2235 for a different comment-reading gap), and without an edit tool the agent defaulted to the only mutation available — add_reply — producing thread noise instead of correcting the original.

Having edit/delete tools also enables agents to clean up their own mistakes programmatically, which is important for production reliability.