OAuth Dynamic Client Registration does not include refresh_token grant type

[fredericlefeurmou]

Description

When ToolHive dynamically registers OAuth clients (RFC 7591), it only requests the authorization_code grant type. This causes token refresh to fail after the initial access token expires (~30-60 minutes) because the OAuth server rejects refresh token requests with:

"The OAuth 2.0 Client is not allowed to use authorization grant 'refresh_token'"

Steps to Reproduce

1. Configure a remote MCP server with OAuth (e.g., Glean)
2. Run thv run to start the MCP server
3. Wait ~30-60 minutes for the initial access token to expire
4. Observe the token refresh fails with the error above

Expected Behavior

Token refresh should work, allowing long-running MCP sessions to maintain authentication.

Proposed Solution

Add refresh_token to the grant_types array in the Dynamic Client Registration request alongside authorization_code.