refactor(layout): 重构应用布局结构

- 将原有布局中的侧边栏和头部组件拆分为独立的 AppSidebar 和 AppHeader 组件
- 移除内联的导航逻辑和样式，交由专用组件管理
- 更新图标库，优化部分图标的显示效果
- 简化认证存储逻辑，增强状态持久化与安全性
- 优化侧边栏状态管理机制，提高响应式体验
- 改进登录流程错误处理，增加网络异常提示
- 调整路由组件结构，提升代码可维护性

src/lib/components/layout/app/AppHeader.svelte

@@ -0,0 +1,60 @@
+<script lang="ts">
+	import { goto } from '$app/navigation';
+	import { resolve } from '$app/paths';
+
+	import Icon from '$lib/components/icon/Icon.svelte';
+	import ThemeSelector from '$lib/widget/ThemeSelector.svelte';
+	import { authStore } from '$lib/stores/authStore.ts';
+	import { toggleSidebar } from '$lib/stores/sidebarStore';
+</script>
+
+<header class="w-full h-18 flex justify-between items-center px-4 bg-base-300 flex-shrink-0">
+	<div>
+		<button
+			class="btn btn-square btn-ghost"
+			onclick={toggleSidebar}
+			aria-label="Toggle Sidebar"
+		>
+			<Icon id="menu" size="24" />
+		</button>
+	</div>
+
+	<div class="flex justify-center items-center gap-4 select-none">
+		<ThemeSelector/>
+
+		{#if $authStore.user }
+			<div class="dropdown dropdown-end ">
+				<div
+					role="button"
+					tabindex="0"
+					class="rounded-full bg-primary h-8 w-8 p-4 flex items-center justify-center text-primary-content font-bold"
+				>
+					{#if $authStore.user.avatar}
+						<img
+							class="w-8 h-8 rounded-full"
+							src="{$authStore.user.avatar}"
+							alt="Avatar"
+						/>
+					{:else}
+						<span>{$authStore.user.nickname.slice(0, 1)}</span>
+					{/if}
+				</div>
+				<div class="dropdown-content mt-2 w-64 shadow-base-300 p-12 shadow-2xl bg-base-200 border border-base-content/10 rounded-box  ">
+						<div class="text-center ">
+							<p class="font-bold">{$authStore.user.nickname}</p>
+							<p class="text-xs mt-2">{$authStore.user.username}</p>
+						</div>
+				</div>
+			</div>
+
+		{:else}
+			<div class="flex items-center">
+				<div class="">
+					<button class="btn btn-primary btn-sm" onclick={() => goto(resolve("/auth/login"))}>
+						登录
+					</button>
+				</div>
+			</div>
+		{/if}
+	</div>
+</header>