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/src/app/p/[token]/steps/payment-step.tsx

@@ -1,9 +1,9 @@
 "use client"
 
-import { Building2, CreditCard, Landmark, Shield, CheckCircle2 } from "lucide-react"
+import { Building2, Landmark, Shield, CheckCircle2 } from "lucide-react"
 
 interface Props {
-  onSelect: (rail: "bank" | "gocardless" | "card") => void
+  onSelect: (rail: "bank" | "gocardless") => void
   amount: number
 }
 
@@ -40,20 +40,6 @@ export function PaymentStep({ onSelect, amount }: Props) {
       highlight: false,
       benefits: ["No action needed", "DD Guarantee"],
     },
-    {
-      id: "card" as const,
-      icon: CreditCard,
-      title: "Card Payment",
-      subtitle: "Visa, Mastercard, Amex — instant",
-      tag: "Instant",
-      tagClass: "bg-purple-100 text-purple-700",
-      detail: "Powered by Stripe. Receipt emailed instantly.",
-      fee: "1.4% + 20p",
-      feeClass: "text-muted-foreground",
-      iconBg: "bg-midnight",
-      highlight: false,
-      benefits: ["Instant confirmation", "All major cards"],
-    },
   ]
 
   return (