🎨 support regenerate thumbnails from UI and improve mobile friendliness

[aaronleopold]

PR contains the following changes:

• Add ability to generate missing thumbnails
• Add ability to force regenerate thumbnails with same or updated config
  • These are definitely in need of a refactor at some point, they aren't bad but there is some code duplication I didn't want to solve right now
• A LOT of UI refactoring to better support mobile views
• Added a new user preference show_query_indicator to essentially render a loading icon whenever a query is being run.
  • I didn't want to enforce this UI element, and figure for those who might find it interesting it could be neat.
• Redesign and simplify error pages and server connection SOS page
• Small redesign of claim page
• Gave the Read More sections a scrollable div on expansion, but it needs to be updated a bit better IMO. Kinda ugly still, but better at least than MASSIVE sections of text lol
• I added a new Explore Books page which just lets you navigate ALL the books you have access to on the server. Comes ready with all the filter options.
  • A bit pedantic, but adding this made me decide to pluralize all of the frontend routing. Otherwise, I'd have /books and /book which is just silly
• Misc docs updates
• Fixed a couple of caching bugs where data 'stays' for too long and jitters between old and new states

After this, I'll probably focus a bit more on the core again