style: improve COD payment card selected state

- Add black border-2 and shadow when selected
- Change icon background to black with white icon when selected
- Add 'Selected' badge with checkmark icon
- Make text bolder and more visible when selected
- Add hover shadow effects
- Add 'selected' translation key for all locales
- Overall more lively and prominent selected state

src/i18n/messages/en.json

@@ -439,6 +439,7 @@
     "securePayment": "Secure payment processing",
     "noMethodsAvailable": "No payment methods available",
     "singleMethodNotice": "Cash on Delivery is the only available payment method for your location",
+    "selected": "Selected",
     "cod": {
       "name": "Cash on Delivery",
       "description": "Pay when you receive your order",