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/src/routes/invoices.ts

@@ -13,8 +13,9 @@ import {
   clients,
   sql,
 } from "@groombook/db";
+import type { AppEnv } from "../middleware/rbac.js";
 
-export const invoicesRouter = new Hono();
+export const invoicesRouter = new Hono<AppEnv>();
 
 const createInvoiceSchema = z.object({
   appointmentId: z.string().uuid().optional(),
@@ -338,3 +339,41 @@ invoicesRouter.patch(
     return c.json({ ...updated, lineItems });
   }
 );
+
+// ─── Refund ───────────────────────────────────────────────────────────────────
+
+import { processRefund } from "../services/payment.js";
+
+const refundSchema = z.object({
+  amountCents: z.number().int().nonnegative().optional(),
+});
+
+invoicesRouter.post(
+  "/:id/refund",
+  zValidator("json", refundSchema),
+  async (c) => {
+    const db = getDb();
+    const staff = c.get("staff");
+    if (!staff) return c.json({ error: "Forbidden" }, 403);
+    if (staff.role !== "manager" && !staff.isSuperUser) {
+      return c.json({ error: "Manager role required" }, 403);
+    }
+
+    const id = c.req.param("id");
+    const body = c.req.valid("json");
+
+    const [invoice] = await db.select().from(invoices).where(eq(invoices.id, id));
+    if (!invoice) return c.json({ error: "Not found" }, 404);
+    if (invoice.status !== "paid") {
+      return c.json({ error: "Refund only allowed on paid invoices" }, 422);
+    }
+    if (!invoice.stripePaymentIntentId) {
+      return c.json({ error: "No Stripe payment intent found for this invoice" }, 422);
+    }
+
+    const result = await processRefund(id, body.amountCents);
+    if (!result) return c.json({ error: "Refund failed" }, 500);
+
+    return c.json({ refundId: result.refundId });
+  }
+);