feat: deferred payments & installment plans — pledge = promise to pay on a date

CORE PRODUCT SHIFT:
A pledge is now a promise to pay on a future date, not just 'pay now'.

NEW FLOW: Amount → Schedule → Payment/Identity → Confirmation

SCHEDULE STEP (/p/[token] step 1):
- 'Pay right now' — existing card/DD/bank flow
- 'Pay on a specific date' — calendar picker with smart suggestions
  (This Friday, End of month, Payday 1st, In 2 weeks, In 1 month)
- 'Split into monthly payments' — 2/3/4/6/12 month installment plans
  with per-installment breakdown and date schedule

SCHEMA CHANGES:
- Pledge.dueDate — when the donor promises to pay (null = now)
- Pledge.planId — groups installment pledges together
- Pledge.installmentNumber / installmentTotal — e.g. 2 of 4
- Pledge.reminderSentForDueDate — tracking flag
- New indexes on dueDate+status and planId

INSTALLMENT PLANS:
- Creates N linked Pledge records with shared planId
- Each installment gets its own reference, due date, reminders
- Reminders: 2 days before, on due date, 3 days after, 10 days after
- WhatsApp receipt shows full plan summary

DEFERRED SINGLE PLEDGES:
- Reminders anchored to due date, not creation date
- 'Pay on date' → reminders: 2 days before, on day, +3d nudge, +10d final
- WhatsApp preferred when phone number provided

DASHBOARD:
- API returns dueDate, planId, installment info for each pledge
- Confirmation step shows schedule details for deferred pledges

pledge-now-pay-later/src/lib/validators.ts

@@ -17,13 +17,18 @@ export const createQrSourceSchema = z.object({
 
 export const createPledgeSchema = z.object({
   amountPence: z.number().int().min(100).max(100000000), // £1 to £1M
-  rail: z.enum(['bank', 'gocardless', 'card', 'fpx']),
+  rail: z.enum(['bank', 'gocardless', 'card']),
   donorName: z.string().max(200).optional().default(''),
   donorEmail: z.string().max(200).optional().default(''),
   donorPhone: z.string().max(20).optional().default(''),
   giftAid: z.boolean().default(false),
   eventId: z.string(),
   qrSourceId: z.string().nullable().optional(),
+  // Payment scheduling
+  scheduleMode: z.enum(['now', 'date', 'installments']).default('now'),
+  dueDate: z.string().optional(),
+  installmentCount: z.number().int().min(2).max(12).optional(),
+  installmentDates: z.array(z.string()).optional(),
 }).transform((data) => ({
   ...data,
   donorEmail: data.donorEmail && data.donorEmail.includes('@') ? data.donorEmail : undefined,