Add update_pull_request_comment and delete_pull_request_comment tools

Beginne damit, das vorhandene add_reply_to_pull_request_comment-Tool und sein GitHub-API-Anfragemuster zu lokalisieren. Füge entsprechende Tools zum Aktualisieren und Löschen hinzu, indem du die angegebenen REST-Endpunkte und Parameter verwendest, und überprüfe anschließend, dass jedes Tool wie beschrieben auf den Kommentar des authentifizierten Benutzers zielt und den angeforderten Body für Aktualisierungen unterstützt.

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.