feat(skills): add baoyu-skills preset repo and auto-supplement missing defaults

- Add JimLiu/baoyu-skills to default skill repositories
- Change init_default_skill_repos() from "first-run only" to "supplement missing"
- New preset repos will now auto-appear for existing users on upgrade

src-tauri/src/services/skill.rs

@@ -128,6 +128,12 @@ impl Default for SkillStore {
                     branch: "master".to_string(),
                     enabled: true,
                 },
+                SkillRepo {
+                    owner: "JimLiu".to_string(),
+                    name: "baoyu-skills".to_string(),
+                    branch: "main".to_string(),
+                    enabled: true,
+                },
             ],
         }
     }