用 Modal 组件替换所有 alert 弹窗

- 创建 ConfirmModal 和 MessageModal 组件
- 更新 App.tsx 使用新的 Modal 组件
- 改进表单验证错误显示
- 提升用户体验和界面一致性

src/renderer/components/ConfirmModal.tsx

@@ -0,0 +1,40 @@
+import React from 'react'
+import './AddProviderModal.css'
+
+interface ConfirmModalProps {
+  title: string
+  message: string
+  confirmText?: string
+  cancelText?: string
+  onConfirm: () => void
+  onCancel: () => void
+}
+
+const ConfirmModal: React.FC<ConfirmModalProps> = ({
+  title,
+  message,
+  confirmText = '确定',
+  cancelText = '取消',
+  onConfirm,
+  onCancel
+}) => {
+  return (
+    <div className="modal-overlay" onClick={onCancel}>
+      <div className="modal-content" onClick={(e) => e.stopPropagation()}>
+        <h2>{title}</h2>
+        <p>{message}</p>
+        
+        <div className="form-actions">
+          <button type="button" className="cancel-btn" onClick={onCancel}>
+            {cancelText}
+          </button>
+          <button type="button" className="submit-btn" onClick={onConfirm}>
+            {confirmText}
+          </button>
+        </div>
+      </div>
+    </div>
+  )
+}
+
+export default ConfirmModal