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>

composer.json

@@ -14,7 +14,6 @@
         "endroid/qr-code-bundle": "*",
         "knplabs/knp-paginator-bundle": "^6.10",
         "knpuniversity/oauth2-client-bundle": "^2.20",
-        "league/flysystem-aws-s3-v3": "^3.32",
         "league/flysystem-bundle": "^3.6",
         "liip/imagine-bundle": "^2.17",
         "mobiledetect/mobiledetectlib": "*",