Add comprehensive logging to debug checkout issues

Added console.log statements to track:
- Client: API response status, data, and errors
- Server: Stripe configuration check, rate limiting, order creation, Stripe session creation

This will help identify exactly where the checkout flow is failing.

Check browser console for client-side errors and server logs for API errors.

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

src/app/checkout/client.tsx

@@ -123,12 +123,15 @@ export default function CheckoutPageClient({ isLoggedIn, customer }: CheckoutPag
                       body: JSON.stringify({ items, customerId: customer.id }),
                     });
                     const data = await res.json();
+                    console.log('Checkout response:', { status: res.status, ok: res.ok, data });
                     if (!res.ok || !data.url) {
                       throw new Error(data.error ?? 'Something went wrong starting checkout.');
                     }
                     window.location.href = data.url;
                   } catch (err) {
-                    setCheckoutError(err instanceof Error ? err.message : 'Something went wrong.');
+                    const errorMsg = err instanceof Error ? err.message : 'Something went wrong.';
+                    console.error('Checkout error:', errorMsg);
+                    setCheckoutError(errorMsg);
                     setCheckingOut(false);
                   }
                 }}