refactor: Skill状态字段从int改为string类型

- model/skill.go: Status字段从 int 改为 string，支持 "active"/"inactive"
- handler/skill_handler.go: 适配Status字段的类型变化，处理"1"/"0"和"active"/"inactive"两种格式
- repository/skill_repo.go: 更新Status字段的空值判断逻辑
- service/skill_service.go: 同步更新

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

server/internal/repository/skill_repo.go

@@ -65,7 +65,7 @@ func (r *SkillRepository) Update(skill *model.Skill) error {
 	if skill.SkillType != "" {
 		updates["skill_type"] = skill.SkillType
 	}
-	if skill.Status != 0 {
+	if skill.Status != "" {
 		updates["status"] = skill.Status
 	}
 	if skill.Path != "" {