Notify When DCR Is Unsupported for Remote MCP Server

When a user attempts to run a remote MCP server using Dynamic Client Registration (DCR), the backend correctly errors out if DCR is not supported by the provider. However, the user receives no indication that DCR is the cause of the failure.

This results in a confusing experience where the operation simply fails without actionable guidance.

Expected Behavior
If DCR is not supported by the remote MCP server, the user should be clearly informed and prompted to use the OAuth 2.0 authorization flow instead.

Actual Behavior
The backend throws an error, but no message is surfaced to the user explaining why the authentication failed.

Proposed Fix

• Detect when the provider does not support DCR
• Surface a user-friendly message such as:
  "This provider does not support Dynamic Client Registration. Please use OAuth 2.0 flow instead."

Impact
This improves user experience by eliminating ambiguity and guiding the user to a supported authentication method.

Start by locating the backend authentication path for remote MCP servers and the error raised when Dynamic Client Registration is unsupported. Trace how that error reaches the user, then surface a message directing them to the OAuth 2.0 authorization flow. Done means the unsupported-DCR case is clearly explained instead of appearing as an unexplained authentication failure.