MCP servers included in Plugins do not initiate OAuth flow

### Short summary

mcp servers included in a plugin do not start the oauth flow

### Affected version or release

v0.2.7

### Installation context

_No response_

### What happened?

Installing the `seismic` plugin from https://github.com/github/revenue-agent-skills and initating the skill in GitHub App with a question like "What does seismic say about EMU trials?" does not initiate the OAuth flow to the seismic MCP Server.

Running `copilot` after the plugin is installed does start the OAuth flow.

### Steps to reproduce

1. I first made sure I removed the existing seismic MCP I had configured and deleted `copilot-mcp-oauth` values from keychain.
2. Install the plugin with `copilot plugin marketplace add github/revenue-agent-skills` and `copilot plugin install seismic@github-revenue`
3. Relaunch GitHub app and ask "what does seismic say about emu trials?". The seismic MCP server oauth flow will not start.
4. Launch `copilot`. The seismic MCP server oauth flow will start.

### Expected behavior

GitHub App should start the MCP OAuth flow for servers defined in plugins

### Additional context

_No response_