Add support for MCP OAuth for Visual Studio (GHE MCP)

### Describe the feature or problem you’d like to solve

Visual Studio cannot connect to GitHub enterprise using OAuth. This is very problematic because PAT access tokens are now restricted to 7 days, on top of being a security issue. (Enterprise policy)

### Proposed solution

It would be highly valuable to pre-authorize this in the 1P Entra ID app for Visual Studio, so OAuth can be enabled by default.

I’m happy to help facilitate this - I can connect you with the right contact in the Visual Studio team if needed.

This change would significantly improve the experience for enterprise users (including Microsoft), who currently need to manually create and rotate GitHub PATs on a regular basis and configure them locally in Visual Studio. Moving to a seamless OAuth flow would remove this friction and align with modern authentication practices.

### Example prompts or workflows (for tools/toolsets only)

We (Microsoft) primarily use Visual Studio (especially after the DevOps migration, where MCP already supported OAuth). Enabling this would let us work without managing recurring GitHub PATs.

### Additional context

VS Code already provides a smooth OAuth experience, and Visual Studio should offer the same. From what we understand, this should only require a change in the 1P app registration.

Feel free to reach out on Teams if helpful.