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/AccountCardList.razor

@@ -0,0 +1,12 @@
+<div class="row g-3">
+    @foreach (var account in Accounts)
+    {
+        <div class="col-sm-6 col-md-4 col-lg-3">
+            <AccountCard Account="account" />
+        </div>
+    }
+</div>
+
+@code {
+    [Parameter] public List<AccountSummaryDto> Accounts { get; set; } = new();
+}