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/state/bookshelf.svelte.ts

@@ -1,4 +1,4 @@
-import { goto, invalidate } from '$app/navigation';
+import { invalidate } from '$app/navigation';
 import { addBooksToShelf, createBookshelf, listBookshelves, removeBooksFromShelf } from '$lib/api';
 import type { Book, Bookshelf } from '$lib/schema';
 import { getContext, setContext } from 'svelte';
@@ -22,7 +22,7 @@ export class BookshelfState {
 
 	async fetchBookshelves(libraryId: string) {
 		try {
-			let paginatedBookshelves = await listBookshelves({
+			const paginatedBookshelves = await listBookshelves({
 				libraries: [libraryId]
 			});
 
@@ -34,7 +34,7 @@ export class BookshelfState {
 
 	async addBookshelf(name: string, libraryId?: string | number, booksToAdd?: string[] | number[]) {
 		try {
-			let bookshelf = await createBookshelf({
+			const bookshelf = await createBookshelf({
 				title: name,
 				library_id: libraryId,
 				book_ids: booksToAdd
@@ -133,7 +133,7 @@ export class BookshelfState {
 						decrementBy++;
 					}
 				});
-				return { ...shelf, total: shelf.total - decrementBy };
+				return { ...shelf, total: (shelf.total ?? 0) - decrementBy };
 			}
 			return shelf;
 		});