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/app_config.rs

@@ -10,7 +10,7 @@ pub struct McpConfig {
 }
 
 /// MCP 根：按客户端分开维护（无历史兼容压力，直接以 v2 结构落地）
-#[derive(Debug, Clone, Serialize, Deserialize)]
+#[derive(Debug, Clone, Serialize, Deserialize, Default)]
 pub struct McpRoot {
     #[serde(default)]
     pub claude: McpConfig,
@@ -18,15 +18,6 @@ pub struct McpRoot {
     pub codex: McpConfig,
 }
 
-impl Default for McpRoot {
-    fn default() -> Self {
-        Self {
-            claude: McpConfig::default(),
-            codex: McpConfig::default(),
-        }
-    }
-}
-
 use crate::config::{copy_file, get_app_config_dir, get_app_config_path, write_json_file};
 use crate::provider::ProviderManager;