fix: replace crypto.randomUUID with generateIdempotencyKey

- Changed purchase flow to use generateIdempotencyKey() which uses secure
  window.crypto.getRandomValues with a math fallback, avoiding secure-context blocks on HTTP
- Log actual error to console in both Buy and Redeem catch blocks

frontend/src/routes/account/+page.svelte

@@ -253,7 +253,8 @@
 				const errText = await res.text();
 				toast.error(errText || 'Failed to redeem gift card');
 			}
-		} catch {
+		} catch (err) {
+			console.error('redeemGiftCard error:', err);
 			toast.error('Network error');
 		} finally {
 			redeemingGiftCard = false;
@@ -283,7 +284,7 @@
 				return;
 			}
 
-			const idempotencyKey = crypto.randomUUID();
+			const idempotencyKey = generateIdempotencyKey();
 
 			const res = await fetch('/api/user/giftcards/buy', {
 				method: 'POST',
@@ -317,7 +318,8 @@
 				const errText = await res.text();
 				toast.error(errText || 'Failed to purchase gift card');
 			}
-		} catch {
+		} catch (err) {
+			console.error('buyGiftCard error:', err);
 			toast.error('Network error');
 		} finally {
 			buyingGiftCard = false;
@@ -452,6 +454,24 @@
 		buyNewCardCVC = formatted;
 	}
 
+	function generateIdempotencyKey(): string {
+		const array = new Uint8Array(16);
+		if (typeof window !== 'undefined' && window.crypto) {
+			window.crypto.getRandomValues(array);
+		} else {
+			for (let i = 0; i < 16; i++) array[i] = Math.floor(Math.random() * 256);
+		}
+		array[6] = (array[6] & 0x0f) | 0x40;
+		array[8] = (array[8] & 0x3f) | 0x80;
+		return [...array]
+			.map((b, i) => {
+				const hex = b.toString(16).padStart(2, '0');
+				if (i === 4 || i === 6 || i === 8 || i === 10) return '-' + hex;
+				return hex;
+			})
+			.join('');
+	}
+
 	async function addCard() {
 		if (!isValidLuhn(newCardNumber) || !/^\d{2}\/\d{2}$/.test(newCardExpiry) || newCardCVC.length < 3) {
 			toast.error('Please fill in all card details correctly');