Add reply to pr comment

[ilyakamens]

Summary

Add a new tool that enables AI agents to reply to existing pull request comments. This tool uses GitHub's CreateCommentInReplyTo REST API to create threaded conversations on pull requests.

(Copied and updated from #723)

Why

Fixes #635

What changed

Features:

• Reply to any existing PR comment using its ID
• Proper error handling for missing parameters and API failures
• Comprehensive test coverage (8 test cases)
• Follows project patterns and conventions
• Registered in pull_requests toolset as a write operation

Parameters:

• owner: Repository owner (required)
• repo: Repository name (required)
• pullNumber: Pull request number (required)
• commentId: ID of comment to reply to (required)
• body: Reply text content (required)

MCP impact

• No tool or API changes
• Tool schema or behavior changed
• New tool added

Prompts tested (tool changes only)

Security / limits

• No security or limits impact
• [] Auth / permissions considered
• [] Data exposure, filtering, or token/size limits considered

Tool renaming

• I am renaming tools as part of this PR (e.g. a part of a consolidation effort)
  • I have added the new tool aliases in deprecated_tool_aliases.go
• I am not renaming tools as part of this PR

Note: if you're renaming tools, you must add the tool aliases. For more information on how to do so, please refer to the official docs.

Lint & tests

• Linted locally with ./script/lint
• Tested locally with ./script/test

Docs

• Not needed
• Updated (README / docs / examples)