refactor(ui): simplify AppSwitcher styles and migrate to local SVG icons

- Replace complex gradient animations with clean, minimal tab design
- Migrate from @lobehub/icons CDN to local SVG assets for better reliability
- Fix clippy warning in error.rs (use inline format args)
- Improve code formatting in skill service and commands
- Reduce CSS complexity in AppSwitcher component (removed blur effects and gradients)
- Update BrandIcons to use imported local SVG files instead of dynamic image loading

This improves performance, reduces external dependencies, and provides a cleaner UI experience.

src-tauri/src/error.rs

@@ -116,6 +116,6 @@ pub fn format_skill_error(
 
     serde_json::to_string(&error_obj).unwrap_or_else(|_| {
         // 如果 JSON 序列化失败，返回简单格式
-        format!("ERROR:{}", code)
+        format!("ERROR:{code}")
     })
 }