feat: 添加可配置的文件上传大小限制

新增 MAX_FILE_SIZE_MB 环境变量统一控制文件上传大小，默认 50MB

docker-compose.dev.yml

@@ -118,6 +118,8 @@ services:
       - MINIO_BUCKET_NAME=${MINIO_BUCKET_NAME:-}
       - MINIO_USE_SSL=${MINIO_USE_SSL:-}
       - WEB_PROXY=${WEB_PROXY:-}
+      # File size limit (in MB)
+      - MAX_FILE_SIZE_MB=${MAX_FILE_SIZE_MB:-50}
     healthcheck:
       test: ["CMD", "grpc_health_probe", "-addr=:50051"]
       interval: 30s