refactor: resolve() internal links instead of plain hrefs

Type-checks every link against the real route tree. Caught a dead one: the
book page linked tags to /tag/{id}, a route that has never existed.

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

@@ -1,3 +1,4 @@
+import { resolve } from '$app/paths';
 import { browser } from '$app/environment';
 import { goto, invalidate } from '$app/navigation';
 import { page } from '$app/state';
@@ -31,7 +32,9 @@ export class LibraryState {
 		this.activeLibrary = this.libraries.find((lib) => lib.id === libraryId) || this.libraries[0];
 		if (browser) {
 			localStorage.setItem('previousLibraryId', this.activeLibrary.id.toString());
-			await goto(`/library/${libraryId}/view`, { invalidate: ['app:libraries'] });
+			await goto(resolve('/(root)/(library)/library/[libraryId]/view', { libraryId: String(libraryId) }), {
+				invalidate: ['app:libraries']
+			});
 		}
 	}