Add Blazor application layer with UI components and pages

- Service interfaces and DTO models
- Dashboard page with account overview
- Account detail page with year/entry management
- Reusable components: AccountCard, EntryTable, YearSelector
- Dialog components: Add/Edit Account, Entry, Transfer, Year
- Main layout and routing configuration

src/Duempelkas.App/Components/Accounts/AccountCard.razor

@@ -0,0 +1,16 @@
+@inject NavigationManager Navigation
+
+<div class="card account-card h-100" @onclick="Navigate">
+    <div class="card-body d-flex flex-column justify-content-between">
+        <h5 class="card-title mb-3">@Account.Name</h5>
+        <div class="@(Account.TotalBalance >= 0 ? "amount-positive" : "amount-negative") fs-4">
+            @($"{Account.TotalBalance:N2} €")
+        </div>
+    </div>
+</div>
+
+@code {
+    [Parameter] public AccountSummaryDto Account { get; set; } = default!;
+
+    private void Navigate() => Navigation.NavigateTo($"/accounts/{Account.Id}");
+}