Add ability to view "branches" for a repo #141

Describe the feature or problem you’d like to solve

I ran into this today, I wanted to get a list of branches for one of the repos in my organization, but the server wasn't able to provide it. You had to already know what the branch was. Now, of course, I can use git to pull that information and look locally, but this feels like something that should be included.

Proposed solution

Add the following functionality to the MCP Server:

curl -L \
  -H "Accept: application/vnd.github+json" \
  -H "Authorization: Bearer <TOKEN>" \
  -H "X-GitHub-Api-Version: 2022-11-28" \
  https://api.github.com/repos/OWNER/REPO/branches

Additional context

n/a