feat(card): add dark theme to Card, Add Card, and Billing Address

• Dark-theme the Card tab empty state, toggle tabs, and screen bg
• Dark-theme Add Card screen (header, form rows, fee summary, CTA)
• Dark-theme Billing Address screen (fields, inputs, save button)
• Dark-theme the billing/shipping address summary card
• Swap the Add Card preview for a branded ahad-card.png image
• Fix loading spinner matching the dark background (invisible)
• Fix a stray borderRadius typo and an icon strokeWidth mismatch

Co-Authored-By: Claude Sonnet 5 noreply@anthropic.com