1.24.1: text search beside the search box, admin fits a phone, the Kobo store limit said plainly

[jularboolean]

Release 1.24.1. Stacked on #63 (the note about the Kobo store), so merging this brings both.

• Admin, Version: the button row wraps, so on a phone "What changed in this version" goes to a new line instead of making the page wider than the screen. Checked at 375 px: no horizontal scroll.
• Search: the "Search inside the books" checkbox stands beside the search box on a wide screen, with the view switch at the far end; on a phone it wraps below the box.
• README: the light and dark library screenshots side by side for everyone.
• From Say plainly that the Kobo store stops working while a Kobo syncs with Legejo #63: the handbook and README say that the Kobo store stops working while a Kobo syncs with Legejo, and how to switch back.
• Release: version 1.24.1, changelog.

184 server tests and 40 web tests pass; web check and build pass. Checked in the browser at desktop and mobile widths.