[BUG] Microsoft 365 MCP OAuth fails - duplicate 'prompt' parameter (AADSTS9000411)

Question

The Microsoft 365 MCP server at microsoft365.mcp.claude.com returns an authorization endpoint URL with `prompt=select_account` baked in. Claude Code's OAuth client then appends `prompt=consent`, resulting in a duplicate parameter.

Azure AD rejects this with: AADSTS9000411: The parameter 'prompt' is duplicated.

Full URL generated:
```
https://login.microsoftonline.com/common/oauth2/v2.0/authorize?prompt=select_account&response_type=code&client_id=...&prompt=consent
```

Related locked issues: #