重构作业结构：优化实体模型、DTO映射和前端界面

- 重构AppMainStruct、AssignmentQuestion、Question等实体模型
- 更新相关DTO以匹配新的数据结构
- 优化前端页面布局和组件
- 添加全局信息和笔记功能相关代码
- 更新数据库迁移和程序配置

TechHelper.Client/Pages/Global/MainStruct/ApplicationMainIconCard.razor

@@ -0,0 +1,11 @@
+<MudPaper Class="d-flex flex-row my-3" Height="@Height" Width="@Width" Elevation="0">
+	<MudIcon Icon="@Icons.Custom.Brands.MudBlazor"  Color="Color.Primary" />
+	<MudText Class="mx-3"><b>TechHelper</b></MudText>
+</MudPaper>
+
+@code {
+	[Parameter]
+	public string Height { get; set; } = "30px";
+	[Parameter]
+	public string Width { get; set; } = "100%";
+}

TechHelper.Client/Pages/Global/MainStruct/SearchBar.razor

@@ -0,0 +1,8 @@
+<MudPaper Class="d-flex flex-grow-1 rounded-xl pl-6" Elevation="0">
+	<MudTextField @bind-Value="TextValue" Label="Search for everything" Variant="Variant.Text"></MudTextField>
+	<MudIconButton Icon="@Icons.Material.Filled.Search"></MudIconButton>
+</MudPaper>
+
+@code {
+	public string TextValue { get; set; }
+}

TechHelper.Client/Pages/Global/MainStruct/SnackErrorBoundary.razor

@@ -0,0 +1,35 @@
+@inherits ErrorBoundary
+@inject ISnackbar Snackbar
+
+@if (CurrentException is null)
+{
+    @ChildContent
+}
+else if (ErrorContent is not null)
+{
+    @ErrorContent(CurrentException)
+}
+else
+{
+    <div class="custom-error-ui">
+        <MudAlert Severity="Severity.Error" Icon="@Icons.Material.Filled.Error">
+            <MudText>组件加载或执行时出现了问题。</MudText>
+            <MudButton Variant="Variant.Filled"
+                       Color="Color.Primary"
+                       Class="mt-3">
+                重试
+            </MudButton>
+        </MudAlert>
+    </div>
+}
+
+
+@code {
+    protected override async Task OnErrorAsync(Exception exception)
+    {
+        Snackbar.Add("操作失败，请重试或联系管理员。", Severity.Error);
+
+        await base.OnErrorAsync(exception);
+    }
+
+}