Test coverage of adding catalogue URLS

### Description

An issue was caught in staging where adding a catalogue URL would crash the browser.

We need to ensure adding/removing URLs has test coverage (and ideally also fail the tests if there are Vue warnings printed to console).

https://github.com/FlowFuse/flowfuse/pull/3012

### Epic/Story

_No response_

### Have you provided an initial effort estimate for this issue?

I have provided an initial effort estimate