Proxima pull request action links to wrong url

### Describe the bug

For example, prompt: review https://octocorp.ghe.com/org/repo/pull/1

It will error with

```json
[{"type":"text","text":"failed to get pull request: GET https://api.octocorp.ghe.com/repos/org/repo/pull/1 404 Not Found []"}]
```

`/repos` should not be in there, I think `api.` also not, but not too sure about that :)

### Affected version

Please run ` docker run -i --rm ghcr.io/github/github-mcp-server ./github-mcp-server --version` and paste the output below

### Steps to reproduce the behavior

Send prompt.

### Expected vs actual behavior

A clear and concise description of what you expected to happen and what actually happened.

Should be able to review the PR.

### Logs

Paste any available logs. Redact if needed.