phsl / new-api

Previously, the "Fetch Model List" button was visible in the channel-creation view even though
it only functions once a channel record exists, leading to user confusion.

Changes introduced:
• Render the "Fetch Model List" button only when editing an existing channel (`isEdit === true`).
• Display an informational Banner in creation mode to remind users that the upstream model list
  can be fetched after the channel has been created.
• Refactored JSX to apply the above conditional rendering without altering existing logic.

This update streamlines the creation workflow and sets clearer expectations for users.