Remove S3/Minio: delete s3_client service, env vars, Minio container, and AWS S3 package

- Remove s3_client service from services.yaml
- Remove S3_* env vars from .env and env.local.j2
- Remove Minio service and volume from docker-compose-dev.yml
- Remove league/flysystem-aws-s3-v3 from composer.json

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.env

@@ -59,11 +59,3 @@ OAUTH_KEYCLOAK_CLIENT_SECRET=changeme
 OAUTH_KEYCLOAK_URL=https://auth.esy-web.dev
 OAUTH_KEYCLOAK_REALM=e-cosplay
 ###< SSO E-Cosplay (Keycloak OIDC) ###
-
-###> s3/minio ###
-S3_ENDPOINT=http://minio:9000
-S3_ACCESS_KEY=e-ticket
-S3_SECRET_KEY=e-ticket
-S3_BUCKET=e-ticket
-S3_REGION=us-east-1
-###< s3/minio ###