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/schema/book.ts

@@ -67,7 +67,7 @@ const identifiersSchema = z
 	.transform((str, ctx) => {
 		try {
 			return JSON.parse(str);
-		} catch (e) {
+		} catch {
 			ctx.addIssue({
 				code: 'custom',
 				message: 'Must be a valid JSON string'