refactor: improve code quality and fix linting issues

- Derive Default trait instead of manual implementation for McpRoot and ProviderManager
- Remove redundant closures in codex_config.rs and config.rs
- Simplify match statements to if let patterns in migration.rs and lib.rs
- Remove unnecessary type conversions and borrows in lib.rs
- Fix i18n key inconsistency: sequentialThinking → sequential-thinking
- Format TypeScript files to match Prettier style

All clippy warnings resolved, code passes all quality checks.

src-tauri/src/provider.rs

@@ -45,21 +45,12 @@ impl Provider {
 }
 
 /// 供应商管理器
-#[derive(Debug, Clone, Serialize, Deserialize)]
+#[derive(Debug, Clone, Serialize, Deserialize, Default)]
 pub struct ProviderManager {
     pub providers: HashMap<String, Provider>,
     pub current: String,
 }
 
-impl Default for ProviderManager {
-    fn default() -> Self {
-        Self {
-            providers: HashMap::new(),
-            current: String::new(),
-        }
-    }
-}
-
 /// 供应商元数据
 #[derive(Debug, Clone, Serialize, Deserialize, Default)]
 pub struct ProviderMeta {