Remove dead Stripe integration

Stripe was wired up but never used:
- No STRIPE_SECRET_KEY in .env
- Card payment step had a 'simulated fallback' that pretended to charge
- Stripe fees (1.4% + 20p) contradict '100% goes to charity' brand promise
- Bank transfer is the primary rail, GoCardless (DD) is the secondary

Removed:
- src/lib/stripe.ts (Stripe client, checkout sessions, webhooks)
- src/app/api/stripe/checkout/route.ts
- src/app/api/stripe/webhook/route.ts
- src/app/p/[token]/steps/card-payment-step.tsx (263 lines)
- 'stripe' and '@stripe/stripe-js' npm packages
- Card option from PaymentStep (payment-step.tsx)
- Card references from confirmation-step.tsx, success/page.tsx
- Stripe from landing page integrations grid
- Stripe from privacy policy sub-processors
- Stripe from terms of service payment references

Type Rail changed: 'bank' | 'gocardless' | 'card' → 'bank' | 'gocardless'
Pledge flow bundle: 19.5kB → 18.2kB (-1.3kB)

Payment options donors now see:
1. Bank Transfer (recommended, zero fees)
2. Direct Debit via GoCardless (1% + 20p, hassle-free)

pledge-now-pay-later/package.json

@@ -12,7 +12,6 @@
     "@auth/prisma-adapter": "^2.11.1",
     "@prisma/adapter-pg": "^7.4.2",
     "@prisma/client": "^7.4.2",
-    "@stripe/stripe-js": "^8.8.0",
     "@types/bcryptjs": "^2.4.6",
     "@types/qrcode": "^1.5.6",
     "bcryptjs": "^3.0.3",
@@ -30,7 +29,6 @@
     "react": "^18",
     "react-dom": "^18",
     "sharp": "^0.34.5",
-    "stripe": "^20.4.0",
     "tailwind-merge": "^3.5.0",
     "zod": "^4.3.6"
   },