feat: 添加配置加载和日志配置支持

- 新增 LogConfig 结构体，支持 9 个日志配置字段（level, encoding, output_stdout, file_path, max_size, max_backups, max_age, compress, gorm_level）

- Config 结构体新增 Log 字段，支持 YAML 解析

- output_stdout 使用 *bool 指针类型，nil 默认为 true

- 更新 config.example.yaml 添加完整 log 配置段

- 新增 TDD 测试：日志配置解析、向后兼容、字段完整性

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

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

internal/config/config.example.yaml

@@ -0,0 +1,16 @@
+server_port: "8080"
+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"
+
+log:
+  level: "info"          # debug, info, warn, error
+  encoding: "json"       # json, console
+  output_stdout: true    # 是否输出日志到终端
+  file_path: ""          # 日志文件路径，留空则不写文件
+  max_size: 100          # max MB per log file
+  max_backups: 5         # number of old log files to retain
+  max_age: 30            # days to retain old log files
+  compress: true         # gzip rotated log files
+  gorm_level: "warn"     # GORM SQL log level: silent, error, warn, info