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/codex_config.rs

@@ -33,7 +33,7 @@ pub fn get_codex_provider_paths(
     provider_name: Option<&str>,
 ) -> (PathBuf, PathBuf) {
     let base_name = provider_name
-        .map(|name| sanitize_provider_name(name))
+        .map(sanitize_provider_name)
         .unwrap_or_else(|| sanitize_provider_name(provider_id));
 
     let auth_path = get_codex_config_dir().join(format!("auth-{}.json", base_name));