style(auth): 优化登录页面样式布局

- 使用 Tailwind CSS 类替换原有基础样式
- 添加背景色和居中对齐容器
- 表单元素增加间距和输入框样式
- 按钮应用宽按钮样式类
- 移除无用的 placeholder 属性
- 调整标签与输入框结构使其更清晰

src/routes/auth/login/+page.svelte

@@ -28,16 +28,16 @@ const handleChange = (e: Event) => {
 }
 </script>
 
-<div class="h-screen w-screen">
-	<form id="loginForm">
-		<div>
-			<label class="" for="username" >	username	</label>
-			<input type="text" name="username" on:change={handleChange} placeholder="username">
-		</div>
-		<div>
-			<label class="" for="password" >	password	</label>
-			<input type="password" name="password" on:change={handleChange} placeholder="password">
-		</div>
-		<button class="" type="submit" on:click="{handleSubmit}" > 登录</button>
+<div class="h-screen w-screen bg-base-300 flex justify-center items-center">
+	<form id="loginForm" class="flex flex-col gap-4">
+
+			<label class="" for="username" >用户名</label>
+			<input class="input" type="text" name="username" on:change={handleChange} >
+
+
+			<label class="" for="password" >密码</label>
+			<input class="input " type="password" name="password" on:change={handleChange} >
+
+			<button class="btn btn-wide" type="submit" on:click="{handleSubmit}" > 登录</button>
 	</form>
 </div>