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/routes/(root)/settings/+layout.svelte

@@ -41,7 +41,7 @@
 		     of libraries; the row above it is overflow-hidden, so without this a
 		     long list is clipped rather than reachable. -->
 		<nav class="flex w-48 shrink-0 flex-col gap-1 overflow-y-auto">
-			{#each items as item}
+			{#each items as item (item.routeId)}
 				<a
 					href={resolve(item.routeId)}
 					class="rounded-md px-3 py-2 text-sm font-medium transition-colors hover:bg-muted {page