[FEATURE] Display why a card was created

[saxoncameron]

When learning some cards, especially cards that have been recursively created, it's not clear to a user why they are learning it.

For example:

Which has no linked words. With the new "primitives of" feature, we can see that it's useful to learn because it's a building block used in some other kanji:

However, that still doesn't tell us WHY we're learning it, and what card/word triggered it to be created. Turns out, it was this card/vocab which, when added, recursively created the unknown primitive cards.

Showing why you're learning the card, e.g. displaying the vocab/card that triggered the card creation, would be really valuable. Could go alongside/nearby the "Appears in" vocab linked words:

but if/when we add this feature in, I'll probably look at restructuring/grouping the data in that section to make things a bit clearer.