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/AddTransferDialog.razor

@@ -0,0 +1,78 @@
+@inject IEntryService EntryService
+@inject IAccountService AccountService
+
+<div class="dialog-backdrop" @onclick="Cancel">
+    <div class="dialog-content" @onclick:stopPropagation="true">
+        <h5 class="mb-3">@(EditEntry != null ? "Umbuchung bearbeiten" : "Neue Umbuchung")</h5>
+
+        <div class="mb-3">
+            <label class="form-label">Zielkonto</label>
+            <select class="form-select" @bind="targetAccountId">
+                <option value="0">— Auswählen —</option>
+                @foreach (var acc in accounts.Where(a => a.Id != SourceAccountId))
+                {
+                    <option value="@acc.Id">@acc.Name</option>
+                }
+            </select>
+        </div>
+
+        <div class="mb-3">
+            <label class="form-label">Datum</label>
+            <input type="date" class="form-control" @bind="date" />
+        </div>
+        <div class="mb-3">
+            <label class="form-label">Bezeichnung</label>
+            <input type="text" class="form-control" @bind="title" placeholder="Beschreibung der Umbuchung" />
+        </div>
+        <div class="mb-3">
+            <label class="form-label">Betrag (€)</label>
+            <input type="number" class="form-control" @bind="amount" step="0.01" min="0.01" />
+        </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="@(!CanSave)"><i class="bi bi-arrow-left-right"></i> @(EditEntry != null ? "Speichern" : "Umbuchen")</button>
+        </div>
+    </div>
+</div>
+
+@code {
+    [Parameter] public int SourceAccountId { get; set; }
+    [Parameter] public EntryDto? EditEntry { get; set; }
+    [Parameter] public EventCallback OnSave { get; set; }
+    [Parameter] public EventCallback OnCancel { get; set; }
+
+    private List<AccountSummaryDto> accounts = new();
+    private int targetAccountId;
+    private DateTime date = DateTime.Today;
+    private string title = string.Empty;
+    private decimal amount;
+
+    private bool CanSave => targetAccountId > 0 && !string.IsNullOrWhiteSpace(title) && amount > 0;
+
+    protected override async Task OnParametersSetAsync()
+    {
+        if (!accounts.Any())
+            accounts = await AccountService.GetAllAccountsAsync();
+
+        if (EditEntry != null)
+        {
+            targetAccountId = EditEntry.LinkedAccountId ?? 0;
+            date = EditEntry.Date;
+            title = EditEntry.Title;
+            amount = EditEntry.Amount;
+        }
+    }
+
+    private async Task Save()
+    {
+        if (EditEntry != null)
+            await EntryService.UpdateTransferAsync(EditEntry.Id, targetAccountId, date, title.Trim(), amount);
+        else
+            await EntryService.CreateTransferAsync(SourceAccountId, targetAccountId, date, title.Trim(), amount);
+        await OnSave.InvokeAsync();
+    }
+
+    private async Task Cancel() => await OnCancel.InvokeAsync();
+}