feat(service): pass work directory to Slurm job submission

Add WorkDir to SubmitJobRequest and pass it as CurrentWorkingDirectory to Slurm REST API. Fixes Slurm 500 error when working directory is not specified.

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

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

internal/model/job.go

@@ -10,6 +10,7 @@ type SubmitJobRequest struct {
 	TimeLimit   string            `json:"time_limit,omitempty"`  // 运行时间限制 (分钟)
 	JobName     string            `json:"job_name,omitempty"`    // 作业名称
 	Environment map[string]string `json:"environment,omitempty"` // 环境变量键值对
+	WorkDir     string            `json:"work_dir,omitempty"`    // 作业工作目录
 }
 
 // JobResponse is the API response for a job.