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/components/mcp/McpFormModal.tsx

@@ -2,7 +2,10 @@ import React, { useState } from "react";
 import { useTranslation } from "react-i18next";
 import { X, Save, AlertCircle, ChevronDown, ChevronUp } from "lucide-react";
 import { McpServer, McpServerSpec } from "../../types";
-import { mcpPresets, getMcpPresetWithDescription } from "../../config/mcpPresets";
+import {
+  mcpPresets,
+  getMcpPresetWithDescription,
+} from "../../config/mcpPresets";
 import { buttonStyles, inputStyles } from "../../lib/styles";
 import McpWizardModal from "./McpWizardModal";
 import {