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/AddAccountDialog.razor

@@ -0,0 +1,29 @@
+<div class="dialog-backdrop" @onclick="Cancel">
+    <div class="dialog-content" @onclick:stopPropagation="true">
+        <h5 class="mb-3">Neues Konto</h5>
+        <div class="mb-3">
+            <label class="form-label">Kontoname</label>
+            <input type="text" class="form-control" @bind="name" @bind:event="oninput"
+                   placeholder="z.B. Girokonto" />
+        </div>
+        <div class="d-flex justify-content-end gap-2">
+            <button class="btn btn-outline-secondary" @onclick="Cancel"><i class="bi bi-x-lg"></i> Abbrechen</button>
+            <button class="btn btn-primary" @onclick="Save" disabled="@string.IsNullOrWhiteSpace(name)"><i class="bi bi-check-lg"></i> Erstellen</button>
+        </div>
+    </div>
+</div>
+
+@code {
+    [Parameter] public EventCallback<string> OnSave { get; set; }
+    [Parameter] public EventCallback OnCancel { get; set; }
+
+    private string name = string.Empty;
+
+    private async Task Save()
+    {
+        if (!string.IsNullOrWhiteSpace(name))
+            await OnSave.InvokeAsync(name.Trim());
+    }
+
+    private async Task Cancel() => await OnCancel.InvokeAsync();
+}