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/Dialogs/ConfirmDialog.razor

@@ -0,0 +1,22 @@
+<div class="dialog-backdrop" @onclick="Cancel">
+    <div class="dialog-content" @onclick:stopPropagation="true">
+        <h5>@Title</h5>
+        <p>@Message</p>
+        <div class="d-flex justify-content-end gap-2">
+            <button class="btn btn-outline-secondary" @onclick="Cancel"><i class="bi bi-x-lg"></i> @CancelText</button>
+            <button class="btn btn-danger" @onclick="Confirm"><i class="bi bi-trash"></i> @ConfirmText</button>
+        </div>
+    </div>
+</div>
+
+@code {
+    [Parameter] public string Title { get; set; } = "Bestätigung";
+    [Parameter] public string Message { get; set; } = "Sind Sie sicher?";
+    [Parameter] public string ConfirmText { get; set; } = "Ja, bestätigen";
+    [Parameter] public string CancelText { get; set; } = "Nein, abbrechen";
+    [Parameter] public EventCallback OnConfirm { get; set; }
+    [Parameter] public EventCallback OnCancel { get; set; }
+
+    private async Task Confirm() => await OnConfirm.InvokeAsync();
+    private async Task Cancel() => await OnCancel.InvokeAsync();
+}