simplify: zakat yes/no per campaign, remove 5 fund types, add I've Donated button for external pledges

- Event.zakatEligible (boolean) replaces Organization.zakatEnabled + 5 fund types
- Pledge.isZakat (boolean) replaces Pledge.fundType enum
- Removed fundAllocation from Event (campaign IS the allocation)
- Identity step: simple checkbox instead of 5-option grid
- Campaign creation: Zakat toggle + optional external URL for self-payment
- External redirect step: 'I've Donated' button calls /api/pledges/[id]/mark-initiated
- Landing page: simplified Zakat section (toggle preview, not 5 fund descriptions)
- Settings: removed org-level Zakat toggle (it's per campaign now)
- Migration: ALTER TABLE adds zakatEligible/isZakat, drops fundAllocation

pledge-now-pay-later/prisma/schema.prisma

@@ -24,7 +24,6 @@ model Organization {
   gcAccessToken   String?
   gcEnvironment   String   @default("sandbox")
   whatsappConnected Boolean @default(false)
-  zakatEnabled    Boolean  @default(false) // enables Zakat / Sadaqah / Lillah fund type picker
   createdAt       DateTime @default(now())
   updatedAt       DateTime @updatedAt
 
@@ -63,7 +62,7 @@ model Event {
   paymentMode      String   @default("self") // self = we show bank details, external = redirect to URL
   externalUrl      String?  // e.g. https://launchgood.com/my-campaign
   externalPlatform String?  // launchgood, enthuse, justgiving, gofundme, other
-  fundAllocation   String?  // e.g. "Mosque Building Fund" — tracks which fund this event raises for
+  zakatEligible    Boolean  @default(false) // is this campaign Zakat-eligible?
   organizationId   String
   organization     Organization @relation(fields: [organizationId], references: [id], onDelete: Cascade)
   createdAt      DateTime @default(now())
@@ -104,7 +103,7 @@ model Pledge {
   donorEmail     String?
   donorPhone     String?
   giftAid        Boolean  @default(false)
-  fundType       String?  // null=general, zakat, sadaqah, lillah, fitrana
+  isZakat        Boolean  @default(false) // donor marked this as Zakat
   iPaidClickedAt DateTime?
   notes          String?