improve category display a little

[pennae]

categories are currently a bit unfriendly to use when they contain many feeds, most of which update rarely. it's not easy to find feeds with unread entries, so it seems prudent to highlight them specially (like feeds with errors are highlighted already), and to sort feeds with unread entries before feeds without unread entries.

Do you follow the guidelines?

• I have tested my changes
• I read this document: https://miniflux.app/faq.html#pull-request

[fguillot]

It would be better to have the same behavior between the feeds list page and the feeds in the category page.

/category/2/feeds:

/feeds:

Also, in Dark mode, the color looks strange to me:

[pennae]

the feeds page is untouched here because #697 stated it's intentionally unsorted for performance. could change it, but it seemed deliberate to not have it that way (and the category list loaded the unread counts anyway, so adding the sort was basically free).

as for the colors, those are what looked least displeasing here. totally open to changing them, but no idea what they should be!

[fguillot]

The performance issue mentioned in #697 is about the SQL query. Your solution solve this problem because the sorting is done after fetching the feeds from the database. It seems more elegant than the Javascript solution proposed in the same discussion.

Actually, your sorting functions could be moved to the storage package: https://github.com/miniflux/v2/blob/master/storage/feed.go#L125-L141

Regarding the colors in Dark mode, I'm not very good at that, every single person will have different taste, but I would try something like that:

[pennae]

your colors are much better. moved the sort to the storage module, and added some css variables to make the unread highlight nicely configurable.