fix: restore cardNum definition in addCard

- Re-added 'const cardNum = newCardNumber.replace(/\s/g, '');' inside addCard
- Log actual error to console in catch block of addCard

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

@@ -477,6 +477,7 @@
 			toast.error('Please fill in all card details correctly');
 			return;
 		}
+		const cardNum = newCardNumber.replace(/\s/g, '');
 		const [monthStr, yearStr] = newCardExpiry.split('/');
 		const month = parseInt(monthStr, 10);
 		const year = 2000 + parseInt(yearStr, 10);
@@ -514,7 +515,8 @@
 				const errText = await res.text();
 				toast.error(errText || 'Failed to add card');
 			}
-		} catch {
+		} catch (err) {
+			console.error('addCard error:', err);
 			toast.error('Network error');
 		} finally {
 			addingCard = false;