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>

docker/nginx/nginx.conf

@@ -28,6 +28,16 @@ http {
             proxy_set_header X-Forwarded-Proto $scheme;
         }
 
+        # AFC Store API — route to Next.js (before Strapi catch-all)
+        location /api/afc/ {
+            proxy_pass http://web;
+            proxy_http_version 1.1;
+            proxy_set_header Host $host;
+            proxy_set_header X-Real-IP $remote_addr;
+            proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
+            proxy_set_header X-Forwarded-Proto $scheme;
+        }
+
         location /api/ {
             proxy_pass http://cms;
             proxy_http_version 1.1;