Allow retrying matrix: URI

e.g. when selecting nheko as my client, my browser prompts me automatically and wants to open the matrix: URI. This works and is great and I can select nheko.

However if I abort, then there is no button to retry this action and I am now stuck (unless I'm smart enough to go back and forth). Thus such a button should exist.

Reproduce the matrix: URI client-selection flow in a browser, then inspect the code handling an aborted client prompt. Add a way to retry the action after cancellation, and verify that selecting a client still opens the URI and that retrying works without navigating back and forth.

Written by the indexing model from the issue text.