feat(config): add WorkDirBase for application job working directory

Add WorkDirBase config field for auto-generated job working directories. Pattern: {base}/{app_name}/{timestamp}_{random}/

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

internal/config/config.example.yaml

@@ -3,6 +3,7 @@ slurm_api_url: "http://localhost:6820"
 slurm_user_name: "root"
 slurm_jwt_key_path: "/etc/slurm/jwt_hs256.key"
 mysql_dsn: "root:@tcp(127.0.0.1:3306)/hpc_platform?parseTime=true"
+work_dir_base: "/mnt/nfs_mount/platform"  # 作业工作目录根路径，留空则不自动创建
 
 log:
   level: "info"          # debug, info, warn, error