feat: add AFC Store with MercadoPago purchases and prize redemption

Players can now buy AfterCoin with real money (MercadoPago Checkout Pro,
$15 MXN/AFC) and redeem AFC for gift cards or cash withdrawals. Admin
fulfills redemptions manually.

- Bridge: payments + redemptions tables, CRUD routes, PATCH auth
- Next.js API: verify-disk, balance, create-preference, webhook (idempotent
  minting with HMAC signature verification), redeem, payment/redemption history
- Frontend: hub, buy flow (4 packages + custom), redeem flow (gift cards +
  cash out), success/failure/pending pages, history with tabs, 8 components
- i18n: full English + Spanish translations
- Infra: nginx /api/afc/ → Next.js, docker-compose env vars, .env.example

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

apps/web/src/app/api/afc/create-preference/route.ts

@@ -0,0 +1,71 @@
+import { NextRequest, NextResponse } from "next/server";
+import { randomUUID } from "crypto";
+import { preferenceClient } from "../lib/mercadopago";
+import { bridgePost, bridgePatch } from "../lib/bridge";
+
+const PRICE_MXN = Number(process.env.AFC_PRICE_MXN) || 15;
+const BASE_URL = process.env.NEXT_PUBLIC_SITE_URL || "http://localhost:3000";
+
+export async function POST(req: NextRequest) {
+  try {
+    const { diskId, amountAfc } = await req.json();
+
+    if (!diskId || !amountAfc || amountAfc < 1) {
+      return NextResponse.json(
+        { error: "diskId and amountAfc (>=1) required" },
+        { status: 400 }
+      );
+    }
+
+    const amountMxn = amountAfc * PRICE_MXN;
+    const paymentId = randomUUID();
+
+    // Create payment record in bridge
+    await bridgePost("/api/payments", {
+      id: paymentId,
+      diskId,
+      amountAfc,
+      amountMxn,
+    });
+
+    // Create MercadoPago preference
+    const preference = await preferenceClient.create({
+      body: {
+        items: [
+          {
+            id: paymentId,
+            title: `${amountAfc} AfterCoin (AFC)`,
+            quantity: 1,
+            unit_price: amountMxn,
+            currency_id: "MXN",
+          },
+        ],
+        external_reference: paymentId,
+        back_urls: {
+          success: `${BASE_URL}/afc/buy/success?payment_id=${paymentId}`,
+          failure: `${BASE_URL}/afc/buy/failure?payment_id=${paymentId}`,
+          pending: `${BASE_URL}/afc/buy/pending?payment_id=${paymentId}`,
+        },
+        auto_return: "approved",
+        notification_url:
+          process.env.MERCADOPAGO_WEBHOOK_URL ||
+          `${BASE_URL}/api/afc/webhook`,
+      },
+    });
+
+    // Store the MP preference ID
+    await bridgePatch(`/api/payments/${paymentId}`, {
+      mp_preference_id: preference.id,
+    });
+
+    return NextResponse.json({
+      paymentId,
+      initPoint: preference.init_point,
+      sandboxInitPoint: preference.sandbox_init_point,
+    });
+  } catch (e: unknown) {
+    const message = e instanceof Error ? e.message : "Unknown error";
+    console.error("create-preference error:", e);
+    return NextResponse.json({ error: message }, { status: 500 });
+  }
+}