feat(decks): Deck-Kategorien über den ganzen Stack

- cards-domain: DECK_CATEGORY_IDS, Labels, DeckCategorySchema,
  category-Feld im DeckSchema
- DB-Schema (decks + marketplace/decks): category-Spalte
- API-Routen: category in create/update/list/explore
- Web: DeckCategoryIcon-Komponente, Kategorie-Picker auf Deck-Detail,
  Kategorie-Icon in DeckListGrid (Marketplace)
- Layout: Bottom-Padding für floating Nav-Bar

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

apps/web/src/lib/components/DeckCategoryIcon.svelte

@@ -0,0 +1,47 @@
+<script lang="ts">
+	import type { DeckCategoryId } from '@cards/domain';
+	import {
+		Globe,
+		Heartbeat,
+		Leaf,
+		Brain,
+		Flag,
+		Medal,
+		Lightning,
+		Palette,
+		MusicNote,
+		Barbell,
+		Sparkle,
+	} from '@mana/shared-icons';
+
+	type Weight = 'thin' | 'light' | 'regular' | 'bold' | 'fill' | 'duotone';
+
+	interface Props {
+		category: DeckCategoryId;
+		size?: number;
+		color?: string | null;
+		weight?: Weight;
+	}
+
+	let { category, size = 32, color = null, weight = 'duotone' }: Props = $props();
+
+	const ICON_MAP: Record<DeckCategoryId, typeof Globe> = {
+		language: Globe,
+		medicine: Heartbeat,
+		science: Leaf,
+		math: Brain,
+		history: Flag,
+		law: Medal,
+		technology: Lightning,
+		arts: Palette,
+		music: MusicNote,
+		sport: Barbell,
+		other: Sparkle,
+	};
+
+	const IconComponent = $derived(ICON_MAP[category]);
+</script>
+
+{#if IconComponent}
+	<IconComponent {size} {weight} color={color ?? undefined} />
+{/if}

apps/web/src/lib/components/marketplace/DeckListGrid.svelte

@@ -1,6 +1,9 @@
 <script lang="ts">
 	import type { DeckListEntry } from '$lib/api/marketplace.ts';
+	import type { DeckCategoryId } from '@cards/domain';
+	import { DECK_CATEGORY_IDS } from '@cards/domain';
 	import AuthorBadge from './AuthorBadge.svelte';
+	import DeckCategoryIcon from '$lib/components/DeckCategoryIcon.svelte';
 
 	interface Props {
 		items: DeckListEntry[];
@@ -9,6 +12,10 @@
 
 	const { items, emptyMessage = 'Noch keine Decks gefunden.' }: Props = $props();
 
+	function isValidCategory(c: string | null): c is DeckCategoryId {
+		return c !== null && (DECK_CATEGORY_IDS as readonly string[]).includes(c);
+	}
+
 	function languageLabel(code: string | null): string {
 		if (!code) return '';
 		const map: Record<string, string> = { de: 'Deutsch', en: 'English', es: 'Español', fr: 'Français' };
@@ -29,14 +36,21 @@
 				<a href="/d/{deck.slug}" class="block">
 					<div class="flex items-start justify-between gap-2">
 						<h3 class="truncate font-medium">{deck.title}</h3>
-						{#if deck.is_featured}
-							<span
-								class="shrink-0 rounded-full bg-[hsl(var(--color-primary))]/15 px-2 py-0.5 text-[10px] font-medium text-[hsl(var(--color-primary))]"
-								title="Editorial Pick"
-							>
-								★ Featured
-							</span>
-						{/if}
+						<div class="flex shrink-0 items-center gap-1.5">
+							{#if isValidCategory(deck.category)}
+								<span class="text-[hsl(var(--color-muted-foreground))]" aria-hidden="true">
+									<DeckCategoryIcon category={deck.category} size={16} weight="duotone" />
+								</span>
+							{/if}
+							{#if deck.is_featured}
+								<span
+									class="rounded-full bg-[hsl(var(--color-primary))]/15 px-2 py-0.5 text-[10px] font-medium text-[hsl(var(--color-primary))]"
+									title="Editorial Pick"
+								>
+									★ Featured
+								</span>
+							{/if}
+						</div>
 					</div>
 					{#if deck.description}
 						<p