feat(GRO-607): Stripe Elements payment UI replacing mock flow

* GRO-605: Stripe SDK integration + payment service

Co-Authored-By: Paperclip <noreply@paperclip.ing>

* GRO-606: Add payment API endpoints (pay invoice, payment methods, refunds)

Co-Authored-By: Paperclip <noreply@paperclip.ing>

* feat(GRO-597): Stripe payment backend — schema, service, API, webhooks

Consolidates GRO-605, GRO-606, GRO-608 into a single clean PR:
- GRO-605: Stripe SDK integration + payment service
- GRO-606: Payment API endpoints (pay invoice, payment methods, refunds)
- GRO-608: Stripe webhook handler

Migration consolidation:
- Single 0026_stripe_payment.sql migration adds stripeCustomerId to clients
  and stripe_payment_intent_id, stripe_refund_id, payment_failure_reason to invoices
- Removed duplicate 0027_stripe_identifiers.sql

Co-Authored-By: Paperclip <noreply@paperclip.ing>

* GRO-607: Install Stripe frontend packages

Co-Authored-By: Paperclip <noreply@paperclip.ing>

* GRO-607: Add /portal/config endpoint + rename date field

Co-Authored-By: Paperclip <noreply@paperclip.ing>

* GRO-607: Replace mock payment flow with real Stripe Elements

Co-Authored-By: Paperclip <noreply@paperclip.ing>

* fix(GRO-607): Stripe Elements payment UI - lint/type fixes

Co-Authored-By: Paperclip <noreply@paperclip.ing>

* fix(GRO-607): remove unused eslint-disable directive in CustomerPortal

Co-Authored-By: Paperclip <noreply@paperclip.ing>

* fix(GRO-607): CTO review fixes — payment security and correctness

- Fix multi-invoice total calculation: use inArray() instead of eq()
  on single ID, sum all invoices not just first
- Add ownership check to payment method deletion: verify the payment
  method belongs to the authenticated Stripe customer before detaching
- Remove duplicate /config endpoint in portal.ts
- Fix webhook Stripe client: use getStripeClient() from payment service
  instead of constructing with WEBHOOK_SECRET
- Remove unnecessary body validator on /invoices/:id/pay route
- Export getStripeClient() for use by stripe-webhooks.ts
- Add inArray import to payment.ts

Co-Authored-By: Paperclip <noreply@paperclip.ing>

---------

Co-authored-by: Paperclip <noreply@paperclip.ing>

apps/api/package.json

@@ -22,6 +22,8 @@
     "hono": "^4.6.17",
     "node-cron": "^3.0.3",
     "nodemailer": "^6.9.16",
+    "stripe": "^22.0.0",
+
     "zod": "^4.3.6"
   },
   "devDependencies": {