简化过度设计，恢复原生弹窗

- 删除 ConfirmModal 和 MessageModal 组件
- 恢复原生 alert() 和 confirm() 弹窗
- 移除不必要的加载状态指示器
- 移除切换供应商的确认对话框
- 简化代码，提升响应速度和用户体验

src/renderer/components/EditProviderModal.tsx

@@ -15,7 +15,6 @@ const EditProviderModal: React.FC<EditProviderModalProps> = ({ provider, onSave,
     apiKey: provider.apiKey
   })
   const [showPassword, setShowPassword] = useState(false)
-  const [error, setError] = useState<string>('')
 
   useEffect(() => {
     setFormData({
@@ -29,7 +28,7 @@ const EditProviderModal: React.FC<EditProviderModalProps> = ({ provider, onSave,
     e.preventDefault()
     
     if (!formData.name || !formData.apiUrl || !formData.apiKey) {
-      setError('请填写所有必填字段')
+      alert('请填写所有必填字段')
       return
     }
 
@@ -53,12 +52,6 @@ const EditProviderModal: React.FC<EditProviderModalProps> = ({ provider, onSave,
         <h2>编辑供应商</h2>
 
         <form onSubmit={handleSubmit}>
-          {error && (
-            <div style={{ color: 'red', marginBottom: '1rem', padding: '0.5rem', backgroundColor: '#ffe6e6', borderRadius: '4px' }}>
-              {error}
-            </div>
-          )}
-          
           <div className="form-group">
             <label htmlFor="name">供应商名称 *</label>
             <input