fix(desktop): 功能验证 6 项缺陷修复

- ISS-002: SkillInfoResponse 增加 source/path 字段，修复技能系统显示 0 个
- ISS-003: Sidebar 添加自动化/技能市场导航入口 + App 返回按钮
- ISS-004: SaaS fetchAvailableModels 添加 .catch() 防限流崩溃
- ISS-006: SaaSSettings/PricingPage 包裹 ErrorBoundary 防白屏
- ISS-008: listModels 加载 localStorage 自定义模型，修复仅显示 1 个模型
- configStore listSkills 映射添加 source/path 转发

desktop/src/lib/kernel-skills.ts

@@ -20,6 +20,8 @@ type SkillItem = {
   enabled: boolean;
   triggers: string[];
   category?: string;
+  source?: string;
+  path?: string;
 };
 
 /** Skill list container shared by list/refresh responses. */