chore: stop lint rules that do not model runes from reporting

no-unused-expressions is off for Svelte files: a bare `book;` in an $effect
declares a dependency. The URL and Set instances it flagged are local
temporaries, marked individually. The one real finding was visibleApiKeys,
genuine reactive state cloned on every mutation to force an update; it is a
SvelteSet now.

frontend/eslint.config.js

@@ -41,8 +41,15 @@ export default defineConfig(
 		// no-useless-assignment joined eslint:recommended in ESLint 10, and its flow analysis
 		// does not model runes: it reads `let { ref = $bindable(null) } = $props()` as a value
 		// that is never read. Deleting the default, as it suggests, breaks the binding.
+		//
+		// no-unused-expressions is off for the same reason: a bare `book;` inside an $effect is
+		// how a reactive dependency is declared when the read would otherwise be untracked.
+		// Removing the statement stops the effect re-running.
 		files: ['**/*.svelte'],
-		rules: { 'no-useless-assignment': 'off' }
+		rules: {
+			'no-useless-assignment': 'off',
+			'@typescript-eslint/no-unused-expressions': 'off'
+		}
 	},
 	{
 		files: ['**/*.svelte', '**/*.svelte.ts', '**/*.svelte.js'],

frontend/src/lib/components/ui/tags-input/tags-input.svelte

@@ -36,7 +36,6 @@
 
 	$effect(() => {
 		// whenever input value changes reset invalid
-		// eslint-disable-next-line @typescript-eslint/no-unused-expressions
 		inputValue;
 
 		untrack(() => {

frontend/src/lib/state/bookCollection.svelte.ts

@@ -105,6 +105,7 @@ export class BookCollectionState {
 
 		this.view = next;
 
+		// eslint-disable-next-line svelte/prefer-svelte-reactivity -- local temporary, not reactive state
 		const url = new URL(page.url);
 		url.searchParams.set('view', next);
 		// Not a route to resolve — this is the current URL with one query param
@@ -138,6 +139,7 @@ export class BookCollectionState {
 
 	updateSearchParams() {
 		// Update URL
+		// eslint-disable-next-line svelte/prefer-svelte-reactivity -- local temporary, not reactive state
 		const url = new URL(window.location.href);
 
 		Object.entries(this.filters).forEach(([filter, values]) => {
@@ -215,6 +217,7 @@ export class BookCollectionState {
 		// and skips every page in between.
 		this.currentBookPage = 1;
 
+		// eslint-disable-next-line svelte/prefer-svelte-reactivity -- local temporary, not reactive state
 		const urlParams = new URLSearchParams(window.location.search);
 
 		// Re-read sort and filter state from URL

frontend/src/lib/state/bookOperations.svelte.ts

@@ -131,6 +131,7 @@ export class BookOperationsState {
 
 	async downloadBooks(bookIds: string[] | number[], filename?: string) {
 		// Construct the download URL
+		// eslint-disable-next-line svelte/prefer-svelte-reactivity -- local temporary, not reactive state
 		const downloadUrl = new URL(`/api/books/download`, page.url.origin);
 		downloadUrl.searchParams.set('library_id', this.libraryId);
 		bookIds.forEach((id) => {
@@ -142,6 +143,7 @@ export class BookOperationsState {
 
 	async downloadBookFile(bookId: number, fileId: number, filename: string) {
 		// Construct the download URL
+		// eslint-disable-next-line svelte/prefer-svelte-reactivity -- local temporary, not reactive state
 		const downloadUrl = new URL(`/api/books/download/${bookId}/${fileId}`, page.url.origin);
 		this.download(downloadUrl, filename);
 	}

frontend/src/lib/state/bookshelf.svelte.ts

@@ -116,6 +116,7 @@ export class BookshelfState {
 		if (!bookshelves) return;
 
 		// Create a Set of shelf IDs that need updating for efficient lookup
+		// eslint-disable-next-line svelte/prefer-svelte-reactivity -- local temporary, not reactive state
 		const shelfIdsToUpdate = new Set<number>();
 		books.forEach((book) => {
 			book.lists.forEach((shelf) => {

frontend/src/routes/(root)/settings/devices/+page.svelte

@@ -21,11 +21,12 @@
 	import { toast } from 'svelte-sonner';
 	import { invalidateAll } from '$app/navigation';
 	import type { Device } from '$lib/schema/device';
+	import { SvelteSet } from 'svelte/reactivity';
 
 	let { data } = $props();
 
 	let createDialogOpen = $state(false);
-	let visibleApiKeys = $state<Set<string>>(new Set());
+	const visibleApiKeys = new SvelteSet<string>();
 	let deleteConfirmDevice = $state<Device | null>(null);
 	let regenerateConfirmDevice = $state<Device | null>(null);
 
@@ -35,7 +36,6 @@
 		} else {
 			visibleApiKeys.add(deviceId);
 		}
-		visibleApiKeys = new Set(visibleApiKeys);
 	}
 
 	function maskApiKey(apiKey: string): string {