Remove quantity field; normalize missing prices to 0,00 €

Each collection row is a unique card (own condition/notes), so quantity
was noise: dropped the field in Directus and removed it from the add
dialog, collection/grid/table views, dashboard stats and sort options.
Cards without Cardmarket data now consistently show 0,00 € (base price
row is always displayed on the card page).

src/lib/collection.ts

@@ -20,9 +20,10 @@ export const variantPriceMap: Record<string, string> = {
 };
 
 /**
- * Resolve the Cardmarket unit price and line total for each collection card.
+ * Resolve the Cardmarket unit price for each collection card.
  * Card details come from the 24h in-memory cache, so repeated cards and
- * repeated page loads don't hit the TCGdex API again.
+ * repeated page loads don't hit the TCGdex API again. Cards without a
+ * Cardmarket price get 0 for consistent display (0,00 €).
  */
 export async function priceCollectionCards(
     cards: MyCard[],
@@ -36,8 +37,7 @@ export async function priceCollectionCards(
                 const priceKey = variantPriceMap[card.variant ?? ""] ?? "avg";
                 price = cardmarket[priceKey] ?? cardmarket.avg ?? 0;
             }
-            const quantity = card.quantity ?? 1;
-            return { ...card, price, totalPrice: price * quantity };
+            return { ...card, price, totalPrice: price };
         }),
     );
 }