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/package.json

@@ -21,7 +21,8 @@
     "marked": "^18.0.3",
     "sql.js": "^1.14.1",
     "@mana/themes": "^0.1.0",
-    "@mana/shared-ui-2": "^0.1.0"
+    "@mana/shared-ui-2": "^0.1.0",
+    "@mana/shared-icons": "^1.0.0"
   },
   "devDependencies": {
     "@sveltejs/adapter-node": "^5.2.0",