chore: clear the mechanical lint and type findings

Dead imports and locals removed, each blocks keyed, `any` narrowed to unknown.
Two context setters kept their calls and lost only the unused binding; the
settings redirect no longer awaits a parent whose data it discards. A leading
underscore now marks a binding that only holds a position.

frontend/src/lib/components/view/book-grid.svelte

@@ -4,7 +4,6 @@
 
 	import type { Book } from '$lib/schema';
 	import BookThumbnail from './book-thumbnail.svelte';
-	import { goto } from '$app/navigation';
 	import { getBookSelectionState } from '$lib/state/bookSelection.svelte';
 	import { getBookOperationsState } from '$lib/state/bookOperations.svelte';
 	import { getLibraryState } from '$lib/state/library.svelte';