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/AccountCard.razor

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+@inject NavigationManager Navigation
+
+<div class="card account-card h-100" @onclick="Navigate">
+    <div class="card-body d-flex flex-column justify-content-between">
+        <h5 class="card-title mb-3">@Account.Name</h5>
+        <div class="@(Account.TotalBalance >= 0 ? "amount-positive" : "amount-negative") fs-4">
+            @($"{Account.TotalBalance:N2} €")
+        </div>
+    </div>
+</div>
+
+@code {
+    [Parameter] public AccountSummaryDto Account { get; set; } = default!;
+
+    private void Navigate() => Navigation.NavigateTo($"/accounts/{Account.Id}");
+}

src/Duempelkas.App/Components/Accounts/AccountCardList.razor

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+<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();
+}

src/Duempelkas.App/Components/Accounts/AccountHeader.razor

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+@* AccountHeader is no longer used - header is now inline in AccountDetail.razor *@

src/Duempelkas.App/Components/Accounts/EntryRow.razor

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+<tr class="@GetRowClass()">
+    <td>@Entry.DisplayId</td>
+    <td>@Entry.Date.ToString("dd.MM.yyyy")</td>
+    <td>
+        @Entry.Title
+        @if (Entry.IsTransfer && !string.IsNullOrEmpty(Entry.LinkedAccountName))
+        {
+            <small class="text-muted ms-1">
+                (@(Entry.Type == EntryType.Expense ? "an" : "von") @Entry.LinkedAccountName)
+            </small>
+        }
+    </td>
+    <td class="text-end @(Entry.Type == EntryType.Income ? "amount-positive" : "amount-negative")">
+        @(Entry.Type == EntryType.Income ? "+" : "\u2212")@($"{Entry.Amount:N2} €")
+    </td>
+    <td>
+        @if (Entry.IsDeleted)
+        {
+            <button class="btn btn-outline-success btn-sm" @onclick="() => OnRestore.InvokeAsync(Entry.Id)" title="Wiederherstellen">
+                <i class="bi bi-arrow-counterclockwise"></i>
+            </button>
+        }
+        else
+        {
+            <div class="d-flex gap-1">
+                <button class="btn btn-outline-secondary btn-sm" @onclick="() => OnEdit.InvokeAsync(Entry.Id)" title="Bearbeiten">
+                    <i class="bi bi-pencil"></i>
+                </button>
+                <button class="btn btn-outline-danger btn-sm" @onclick="() => OnDelete.InvokeAsync(Entry.Id)" title="Löschen">
+                    <i class="bi bi-trash"></i>
+                </button>
+            </div>
+        }
+    </td>
+</tr>
+
+@code {
+    [Parameter] public EntryDto Entry { get; set; } = default!;
+    [Parameter] public EventCallback<int> OnDelete { get; set; }
+    [Parameter] public EventCallback<int> OnRestore { get; set; }
+    [Parameter] public EventCallback<int> OnEdit { get; set; }
+
+    private string GetRowClass()
+    {
+        var classes = new List<string>();
+        if (Entry.IsTransfer) classes.Add("entry-row-transfer");
+        if (Entry.IsDeleted) classes.Add("entry-deleted");
+        return string.Join(" ", classes);
+    }
+}

src/Duempelkas.App/Components/Accounts/EntryTable.razor

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+<div class="table-responsive">
+    <table class="table table-hover table-sm align-middle">
+        <thead class="table-light">
+            <tr>
+                <th style="width: 100px;">LfdNr</th>
+                <th style="width: 120px;">Datum</th>
+                <th>Bezeichnung</th>
+                <th style="width: 140px;" class="text-end">Betrag</th>
+                <th style="width: 80px;"></th>
+            </tr>
+        </thead>
+        <tbody>
+            @foreach (var entry in Entries)
+            {
+                <EntryRow Entry="entry" OnDelete="OnDeleteEntry" OnRestore="OnRestoreEntry" OnEdit="OnEditEntry" />
+            }
+        </tbody>
+    </table>
+</div>
+
+@if (!Entries.Any())
+{
+    <div class="text-center py-3 text-muted">Keine Einträge vorhanden.</div>
+}
+
+@code {
+    [Parameter] public List<EntryDto> Entries { get; set; } = new();
+    [Parameter] public EventCallback<int> OnDeleteEntry { get; set; }
+    [Parameter] public EventCallback<int> OnRestoreEntry { get; set; }
+    [Parameter] public EventCallback<int> OnEditEntry { get; set; }
+}

src/Duempelkas.App/Components/Accounts/ExportButton.razor

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+@* ExportButton is no longer used - export is now inline in AccountDetail.razor *@

src/Duempelkas.App/Components/Accounts/YearSelector.razor

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+@* YearSelector is no longer used - year selection has been removed from the data model. *@