feat: add CmsGenreBrowser genre browse mode to CMS track list

fix: add @key="ExpandedGenre" to CmsTrackGrid so genre switch forces fresh component instance

DeepDrftManager/Components/Pages/Tracks/CmsGenreBrowser.razor

@@ -0,0 +1,52 @@
+@using DeepDrftModels.DTOs
+
+@if (IsLoading)
+{
+    <MudProgressCircular Indeterminate="true" Class="mt-4" />
+}
+else if (Genres.Count == 0)
+{
+    <MudText Typo="Typo.body1" Class="mt-4">No genres found.</MudText>
+}
+else
+{
+    <MudGrid Spacing="3" Class="mt-2">
+        @foreach (var genre in Genres)
+        {
+            var isExpanded = ExpandedGenre == genre.Genre;
+            <MudItem xs="12" sm="6" md="4">
+                <MudCard Elevation="@(isExpanded ? 4 : 1)"
+                         Style="cursor: pointer;"
+                         @onclick="@(() => ToggleGenre(genre.Genre))">
+                    <div class="@SwatchClass(isExpanded)"></div>
+                    <MudCardContent>
+                        <MudText Typo="Typo.h6">@genre.Genre</MudText>
+                        <MudText Typo="Typo.body2" Class="mud-text-secondary">@genre.TrackCount track(s)</MudText>
+                    </MudCardContent>
+                </MudCard>
+            </MudItem>
+        }
+    </MudGrid>
+
+    @if (ExpandedGenre is not null)
+    {
+        <MudDivider Class="my-4" />
+        <MudText Typo="Typo.h6" Class="mb-2">@ExpandedGenre</MudText>
+        <CmsTrackGrid @key="ExpandedGenre" GenreFilter="ExpandedGenre" ShowAddButton="false" />
+    }
+}
+
+@code {
+    [Parameter] public IReadOnlyList<GenreSummaryDto> Genres { get; set; } = Array.Empty<GenreSummaryDto>();
+    [Parameter] public bool IsLoading { get; set; }
+    [Parameter] public string? ExpandedGenre { get; set; }
+    [Parameter] public EventCallback<string?> OnExpandedGenreChanged { get; set; }
+
+    // The view model owns the toggle (selecting the open genre collapses it), so we pass the raw
+    // clicked genre rather than pre-computing the next state here — keeps the toggle logic single-sourced.
+    private async Task ToggleGenre(string genre) =>
+        await OnExpandedGenreChanged.InvokeAsync(genre);
+
+    private static string SwatchClass(bool isExpanded) =>
+        isExpanded ? "cms-genre-swatch cms-genre-swatch--active" : "cms-genre-swatch";
+}

DeepDrftManager/Components/Pages/Tracks/CmsGenreBrowser.razor.css

@@ -0,0 +1,10 @@
+.cms-genre-swatch {
+    width: 100%;
+    height: 80px;
+    background-color: var(--mud-palette-action-default-hover);
+    transition: background-color 0.2s ease;
+}
+
+.cms-genre-swatch--active {
+    background-color: var(--mud-palette-primary-hover);
+}

DeepDrftManager/Components/Pages/Tracks/TrackList.razor

@@ -57,7 +57,10 @@
     }
     else
     {
-        <MudAlert Severity="Severity.Info" Class="mt-4">Genre browser — coming in the next wave.</MudAlert>
+        <CmsGenreBrowser Genres="VM.Genres"
+                         IsLoading="VM.GenresLoading"
+                         ExpandedGenre="VM.ExpandedGenre"
+                         OnExpandedGenreChanged="OnExpandedGenreChanged" />
     }
 </MudContainer>
 
@@ -93,6 +96,12 @@
         StateHasChanged();
     }
 
+    private void OnExpandedGenreChanged(string? genre)
+    {
+        VM.SetExpandedGenre(genre);
+        StateHasChanged();
+    }
+
     /// <summary>
     /// Backfill every track missing a waveform profile, one request at a time so a large backfill
     /// does not flood the API with concurrent WAV decodes. On completion, refreshes the grid's