Enterprise accounts using github-mcp-server failed

### Describe the bug

When signed in to an enterprise account, tool calls using `github-mcp-server` uses the enterprise URL and fails for external lookups, but doenst look like it falls back to standard github url and just uses a standard web fetch instead of the MCP server

```
✗ Get file or directory contents (MCP: github-mcp-server) · docs/auth/index.md · owner: "github", repo: "copilot-sdk", path: "docs/auth/index.md"
└ MCP server 'github-mcp-server': failed to resolve git reference: failed to get repository info: GET https://api.ictcardiffcouncil.ghe.com/repos/github/copilot-sdk: 404 Not Found []

● Fetching web content https://raw.githubusercontent.com/github/copilot-sdk/main/docs/auth/index.md · max_length: 10000, raw: true, url: "https://raw.githubusercontent.com/github/copilot-…
└ Here is the raw content:
```

### Affected version

_No response_

### Steps to reproduce the behavior

_No response_

### Expected behavior

_No response_

### Additional context

_No response_

Reproduce the shown docs/auth/index.md lookup while signed in to an enterprise account, using github-mcp-server. Trace how the enterprise URL is selected and how external repository lookups fall back to the standard GitHub path. Done means the lookup no longer fails at the enterprise URL and uses the intended MCP or standard fetch behavior.

Written by the indexing model from the issue text.