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/EditCarryoverDialog.razor

@@ -0,0 +1,27 @@
+<div class="dialog-backdrop" @onclick="Cancel">
+    <div class="dialog-content" @onclick:stopPropagation="true">
+        <h5 class="mb-3">Übertrag bearbeiten</h5>
+        <div class="mb-3">
+            <label class="form-label">Übertrag (€)</label>
+            <input type="number" class="form-control" step="0.01" @bind="amount" />
+        </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"><i class="bi bi-check-lg"></i> Speichern</button>
+        </div>
+    </div>
+</div>
+
+@code {
+    [Parameter] public decimal CurrentAmount { get; set; }
+    [Parameter] public EventCallback<decimal> OnSave { get; set; }
+    [Parameter] public EventCallback OnCancel { get; set; }
+
+    private decimal amount;
+
+    protected override void OnParametersSet() => amount = CurrentAmount;
+
+    private async Task Save() => await OnSave.InvokeAsync(amount);
+
+    private async Task Cancel() => await OnCancel.InvokeAsync();
+}