feat: 添加业务服务层和结构化日志

- JobService: 提交、查询、取消、历史记录，记录关键操作日志

- ClusterService: 节点、分区、诊断查询，记录错误日志

- NewSlurmClient: JWT 认证 HTTP 客户端工厂

- 所有构造函数接受 *zap.Logger 参数实现依赖注入

- 提交/取消成功记录 Info，API 错误记录 Error

- 完整 TDD 测试，使用 zaptest/observer 验证日志输出

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

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

internal/service/slurm_client.go

@@ -0,0 +1,15 @@
+package service
+
+import (
+	"gcy_hpc_server/internal/slurm"
+)
+
+// NewSlurmClient creates a Slurm SDK client with JWT authentication.
+// It reads the JWT key from the given keyPath and signs tokens automatically.
+func NewSlurmClient(apiURL, userName, jwtKeyPath string) (*slurm.Client, error) {
+	return slurm.NewClientWithOpts(
+		apiURL,
+		slurm.WithUsername(userName),
+		slurm.WithJWTKey(jwtKeyPath),
+	)
+}