feat: add missing pull request operations to GitHub server

[chrisguillory]

Description

This PR adds missing pull request operations that were already implemented in operations/pulls.ts but not exposed in index.ts. The added operations are:

• get_pull_request
• list_pull_requests
• create_pull_request_review
• merge_pull_request
• get_pull_request_files
• get_pull_request_status
• update_pull_request_branch
• get_pull_request_comments
• get_pull_request_reviews

Server Details

• Server: github
• Changes to: tools (exposing existing operations)

Motivation and Context

The GitHub server already had these pull request operations implemented in operations/pulls.ts, but they weren't exposed in index.ts. This change makes these useful operations available to users of the GitHub MCP server.

How Has This Been Tested?

[ ] These operations were already implemented and tested in the pulls.ts file. Additional testing would be beneficial.

Breaking Changes

No breaking changes. This PR only adds new operations.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Checklist

• I have read the MCP Protocol Documentation
• My changes follows MCP security best practices
• I have updated the server's README accordingly
• I have tested this with an LLM client
• My code follows the repository's style guidelines
• New and existing tests pass locally
• I have added appropriate error handling
• I have documented all environment variables and configuration options

Additional context

This PR was created by Claude Desktop (Claude 3.5 Sonnet) to expose existing functionality that was already implemented but not exposed through the server's interface.

[apeatling]

Came here to +1 this PR since I'm in need of the extra PR functionality this provides.

[chrisguillory]

@jspahrsummers Can you request a PR review? I don't appear to have access.