## Bug

When setting up an OAuth2 GitHub App-based MCP server (using client_id/secret, not PAT), the OAuth callback redirects to a non-existent page:

``` https://<base_url>/ui/mcp/oauth/callback?code=<code>&state=<state> ```

This page does not exist in the LiteLLM UI, resulting in a 404.

## Steps to Reproduce

1. Create an MCP server with OAuth2 auth (GitHub App with client_id + client_secret) 2. Register callback URL as `<base_url>/callback` with GitHub 3. Initiate OAuth flow from the LiteLLM UI 4. After GitHub authorization, the browser redirects to `/ui/mcp/oauth/callback` instead of the registered `/callback` endpoint

## Expected Behavior

The OAuth callback should redirect to a URL that: 1. Exists in the LiteLLM proxy/UI 2. Matches what can be registered as a callback URL with the OAuth provider 3. Completes the token exchange and stores credentials

## Environment

- LiteLLM version: latest (main branch) - MCP server type: GitHub App (OAuth2 with client_id/secret)