fix(deploy): use quay.io/minio images (Docker Hub minio/minio delisted)

minio/minio and minio/mc are no longer pullable from Docker Hub; use
quay.io/minio/minio for both the server and the one-shot bucket-init step
(mc ships bundled inside the minio image).

Claude-Session: https://claude.ai/code/session_01F1M1Jic1wTSn4igUENynmZ

backend/docker-compose.prod.yml

@@ -27,7 +27,7 @@ services:
       retries: 10
 
   minio:
-    image: minio/minio
+    image: quay.io/minio/minio:latest
     restart: unless-stopped
     command: server /data
     environment:
@@ -43,7 +43,7 @@ services:
       retries: 10
 
   minio-init:
-    image: minio/mc
+    image: quay.io/minio/minio:latest
     depends_on:
       minio:
         condition: service_healthy