refactor(storage): remove MinIO backend, filesystem-only storage

Remove the MinIO/S3 storage backend entirely. The filesystem backend is
fully implemented, already used in production, and a migrate-storage tool
exists for any remaining MinIO deployments to migrate beforehand.

Changes:
- Delete MinIO client implementation (internal/storage/storage.go)
- Delete migrate-storage tool (cmd/migrate-storage, scripts/migrate-storage.sh)
- Remove MinIO service, volumes, and env vars from all Docker Compose files
- Simplify StorageConfig: remove Endpoint, AccessKey, SecretKey, Bucket,
  UseSSL, Region fields; add SILO_STORAGE_ROOT_DIR env override
- Change all SQL COALESCE defaults from 'minio' to 'filesystem'
- Add migration 020 to update column defaults to 'filesystem'
- Remove minio-go/v7 dependency (go mod tidy)
- Update all config examples, setup scripts, docs, and tests

deployments/docker-compose.yaml

@@ -19,26 +19,6 @@ services:
     networks:
       - silo-network
 
-  minio:
-    image: minio/minio:RELEASE.2023-05-04T21-44-30Z
-    container_name: silo-minio
-    command: server /data --console-address ":9001"
-    environment:
-      MINIO_ROOT_USER: ${MINIO_ACCESS_KEY:-silominio}
-      MINIO_ROOT_PASSWORD: ${MINIO_SECRET_KEY:-silominiosecret}
-    volumes:
-      - minio_data:/data
-    ports:
-      - "9000:9000"
-      - "9001:9001"
-    healthcheck:
-      test: ["CMD", "curl", "-f", "http://localhost:9000/minio/health/live"]
-      interval: 10s
-      timeout: 5s
-      retries: 5
-    networks:
-      - silo-network
-
   silo:
     build:
       context: ..
@@ -47,19 +27,12 @@ services:
     depends_on:
       postgres:
         condition: service_healthy
-      minio:
-        condition: service_healthy
     environment:
       SILO_DB_HOST: postgres
       SILO_DB_PORT: 5432
       SILO_DB_NAME: silo
       SILO_DB_USER: silo
       SILO_DB_PASSWORD: ${POSTGRES_PASSWORD:-silodev}
-      SILO_MINIO_ENDPOINT: minio:9000
-      SILO_MINIO_ACCESS_KEY: ${MINIO_ACCESS_KEY:-silominio}
-      SILO_MINIO_SECRET_KEY: ${MINIO_SECRET_KEY:-silominiosecret}
-      SILO_MINIO_BUCKET: silo-files
-      SILO_MINIO_USE_SSL: "false"
       SILO_SESSION_SECRET: ${SILO_SESSION_SECRET:-change-me-in-production}
       SILO_OIDC_CLIENT_SECRET: ${SILO_OIDC_CLIENT_SECRET:-}
       SILO_LDAP_BIND_PASSWORD: ${SILO_LDAP_BIND_PASSWORD:-}
@@ -68,6 +41,7 @@ services:
     ports:
       - "8080:8080"
     volumes:
+      - silo_data:/var/lib/silo/data
       - ../schemas:/etc/silo/schemas:ro
       - ./config.dev.yaml:/etc/silo/config.yaml:ro
     healthcheck:
@@ -80,7 +54,7 @@ services:
 
 volumes:
   postgres_data:
-  minio_data:
+  silo_data:
 
 networks:
   silo-network: