fix: hide empty description and fix broken skill link for skills.sh results

- Hide "暂无描述" text when skill has no description (skills.sh API
  doesn't return descriptions), show empty spacer instead
- Change skills.sh result link from guessed subdirectory path to repo
  root URL, since skillId doesn't reflect the actual nested path

src-tauri/src/services/skill.rs

@@ -2738,8 +2738,8 @@ impl SkillService {
                     repo_branch: "main".to_string(),
                     installs: s.installs,
                     readme_url: Some(format!(
-                        "https://github.com/{}/{}/tree/main/{}",
-                        owner, repo, s.skill_id
+                        "https://github.com/{}/{}",
+                        owner, repo
                     )),
                 })
             })