Issue 497 fix + Issue 476 fix + Issue 465 feature + Issue 489 fix + Issue 501 fix

Closes #497, #476, #465, #489, and #501

See merge request inp-net/churros!51

fix: inscriptions en masse: tolère pas les doubles espaces, ne clear pas les résultats d'inscription à un second essai (closes #507)

thanks to http 301 redirect caching, i _have_ to do this…

why didn't i do this before??? beats me

fix: add a warning message for older users

See merge request inp-net/churros!46

Close #514

fix(CardGroup): avoid small gaps in cover image

Closes #508

See merge request inp-net/churros!53

Close #508