feat: manage_skill + 全局 skills 目录

新增:
- manage_skill: LLM 可调用的 Skill 创建/删除/列出工具 (High)
- 全局 skills 支持: ~/.ias/skills/ 自动加载
- SkillRegistry::register_skill() 动态注册
- SkillRegistry::load() 三元加载: system → global → user

manage_skill 操作:
  create: 写 SKILL.md + 执行脚本到 skills/<name>/
  delete: 移除 skills/<name>/
  list: 列出所有自定义 Skill

目前一共 9 个系统 Skills

src/tools/parser.rs

@@ -211,10 +211,11 @@ mod tests {
         ));
         match result {
             Ok(registry) => {
-                assert_eq!(registry.count(), 8, "应该有 8 个系统技能");
+                assert_eq!(registry.count(), 9, "应该有 9 个系统技能");
                 let names: Vec<&str> = registry.list_specs().iter().map(|s| s.name.as_str()).collect();
                 println!("已加载技能: {:?}", names);
                 assert!(names.contains(&"manage_memos"));
+                assert!(names.contains(&"manage_skill"));
                 assert!(names.contains(&"get_current_datetime"));
                 assert!(names.contains(&"query_weather"));
                 assert!(names.contains(&"search_web"));