refactor(staples): move household/staples route into (app) group — adds sidebar nav

Onboarding context uses fixed inset overlay to cover AppShell.
Settings context inherits AppShell layout by default.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/routes/(app)/household/staples/+page.svelte

@@ -14,7 +14,7 @@
 </svelte:head>
 
 {#if isOnboarding}
-	<div class="flex min-h-screen bg-[var(--color-page)]">
+	<div class="fixed inset-0 z-50 flex bg-[var(--color-page)]">
 		<!-- Desktop sidebar -->
 		<aside class="hidden md:flex w-[300px] flex-shrink-0 flex-col bg-[var(--color-surface)] border-r border-[var(--color-border)] p-[40px_28px]">
 			<ProgressSidebar currentStep={2} />
@@ -44,9 +44,9 @@
 		</main>
 	</div>
 {:else}
-	<div class="flex min-h-screen flex-col bg-[var(--color-page)]">
+	<div class="p-[16px_20px] md:p-[40px_56px]">
 		{#if data.ctx === 'settings'}
-			<a href="/settings" class="font-[var(--font-sans)] text-[12px] text-[var(--color-text-muted)] hover:text-[var(--color-text)] mb-2 inline-block">← Einstellungen</a>
+			<a href="/settings" class="font-[var(--font-sans)] text-[12px] text-[var(--color-text-muted)] hover:text-[var(--color-text)] mb-4 inline-block">← Einstellungen</a>
 		{/if}
 		<h1 class="mb-[8px] font-[var(--font-display)] text-[18px] font-medium md:text-[28px] text-[var(--color-text)]">Vorräte</h1>
 		<StaplesManager categories={data.categories} context="settings" />