facia-tool Show where other stories are on the same front

What's changed?

While shadowing a Digital Editor working on the Network Fronts, I noticed a few times where cards were being dragged from a container to the clipboard, and then from the clipboard to another container on the same Front. They would then need to remember to scroll back to the old container and remove the old card to avoid duplication on the Front. Sometimes, the editor said, it was easy to forget to do this, or you wouldn't even realise as the front was handed over in that state.

To avoid editors having to keep a mental model of which cards were in multiple containers, this PR surfaces which cards are elsewhere on the same Front within the UI:

This should hopefully reduce the cognitive load and number of duplication mistakes.

The logic used to derive CardsWhichAreAlsoOnOtherCollectionsOnSameFront is similar to the CollectionsWhichAreAlsoOnOtherFronts logic made clearer in #1887 and #1888. There are tests and you can also have a play with it yourself in the UI (you will need to enable the feature switch in e.g. https://fronts.local.dev-gutools.co.uk/v2/features).