feat(cms): add Track Browser foundation with mode toggle and CmsTrackGrid

- Extend ICmsTrackService.GetPagedAsync with album/genre filter params
- Add CmsTrackBrowserViewModel (DI-scoped) with lazy album/genre load
- Extract CmsTrackGrid: 9-column layout, waveform status, per-row generate,
  info tooltip, album/genre filter params, OnStatusLoaded callback
- Restructure TrackList: remove MudTabs, add three @page routes, mode toggle,
  Generate All Missing button; album/genre stubs for next wave

DeepDrftManager/Services/CmsTrackBrowserViewModel.cs

@@ -0,0 +1,73 @@
+using DeepDrftModels.DTOs;
+
+namespace DeepDrftManager.Services;
+
+/// <summary>The three browse dimensions for the /tracks page.</summary>
+public enum BrowseMode
+{
+    Tracks,
+    Albums,
+    Genres,
+}
+
+/// <summary>
+/// Holds the /tracks browser's current mode plus the album- and genre-mode datasets. Scoped per
+/// circuit. Album and genre lists are fetched lazily on first switch into their mode and cached for
+/// the circuit's lifetime; Track mode owns its own paging inside <c>CmsTrackGrid</c> and needs no
+/// state here.
+/// </summary>
+public class CmsTrackBrowserViewModel
+{
+    private readonly ICmsTrackService _trackService;
+
+    public CmsTrackBrowserViewModel(ICmsTrackService trackService)
+    {
+        _trackService = trackService;
+    }
+
+    public BrowseMode Mode { get; private set; } = BrowseMode.Tracks;
+
+    // Album mode.
+    public IReadOnlyList<ReleaseDto> Albums { get; private set; } = Array.Empty<ReleaseDto>();
+    public bool AlbumsLoading { get; private set; }
+
+    // Genre mode.
+    public IReadOnlyList<GenreSummaryDto> Genres { get; private set; } = Array.Empty<GenreSummaryDto>();
+    public bool GenresLoading { get; private set; }
+    public string? ExpandedGenre { get; private set; }
+
+    /// <summary>
+    /// Switch the active mode, lazily loading the album or genre dataset on first entry. Collapses
+    /// any expanded genre row. The grid in Track mode owns its own data, so no fetch happens there.
+    /// </summary>
+    public async Task SwitchModeAsync(BrowseMode mode)
+    {
+        Mode = mode;
+        ExpandedGenre = null; // collapse on mode switch
+
+        if (mode == BrowseMode.Albums && Albums.Count == 0 && !AlbumsLoading)
+        {
+            AlbumsLoading = true;
+            var result = await _trackService.GetReleasesAsync();
+            Albums = result.Success && result.Value is not null
+                ? result.Value
+                : Array.Empty<ReleaseDto>();
+            AlbumsLoading = false;
+        }
+        else if (mode == BrowseMode.Genres && Genres.Count == 0 && !GenresLoading)
+        {
+            GenresLoading = true;
+            var result = await _trackService.GetGenreSummariesAsync();
+            Genres = result.Success && result.Value is not null
+                ? result.Value
+                : Array.Empty<GenreSummaryDto>();
+            GenresLoading = false;
+        }
+    }
+
+    /// <summary>Toggle the expanded genre row. Selecting the already-expanded genre collapses it.</summary>
+    public void SetExpandedGenre(string? genre)
+    {
+        ExpandedGenre = ExpandedGenre == genre ? null : genre;
+    }
+}

DeepDrftManager/Services/CmsTrackService.cs

@@ -154,6 +154,7 @@ public class CmsTrackService : ICmsTrackService
 
     public async Task<ResultContainer<PagedResult<TrackDto>>> GetPagedAsync(
         int page, int pageSize, string? sortColumn, bool sortDescending,
+        string? album = null, string? genre = null,
         CancellationToken ct = default)
     {
         var client = _httpClientFactory.CreateClient(ContentCmsClientName);
@@ -162,6 +163,14 @@ public class CmsTrackService : ICmsTrackService
         {
             query += $"&sortColumn={Uri.EscapeDataString(sortColumn)}";
         }
+        if (!string.IsNullOrWhiteSpace(album))
+        {
+            query += $"&album={Uri.EscapeDataString(album)}";
+        }
+        if (!string.IsNullOrWhiteSpace(genre))
+        {
+            query += $"&genre={Uri.EscapeDataString(genre)}";
+        }
 
         HttpResponseMessage response;
         try
@@ -542,7 +551,7 @@ public class CmsTrackService : ICmsTrackService
     {
         // Re-use the paged endpoint: a single-item page carries the full TotalCount, so no
         // dedicated count endpoint is needed.
-        var paged = await GetPagedAsync(page: 1, pageSize: 1, sortColumn: null, sortDescending: false, ct);
+        var paged = await GetPagedAsync(page: 1, pageSize: 1, sortColumn: null, sortDescending: false, ct: ct);
         if (!paged.Success || paged.Value is null)
         {
             var error = paged.Messages.FirstOrDefault()?.Message ?? "Failed to load track count.";

DeepDrftManager/Services/ICmsTrackService.cs

@@ -41,10 +41,13 @@ public interface ICmsTrackService
     Task<Result> DeleteTrackAsync(long id, CancellationToken ct = default);
 
     /// <summary>
-    /// Fetch a page of track metadata from the Content API's <c>GET api/track/page</c>.
+    /// Fetch a page of track metadata from the Content API's <c>GET api/track/page</c>. Optional
+    /// <paramref name="album"/> and <paramref name="genre"/> filters narrow the result to a single
+    /// release title or genre; null leaves the dimension unfiltered.
     /// </summary>
     Task<ResultContainer<PagedResult<TrackDto>>> GetPagedAsync(
         int page, int pageSize, string? sortColumn, bool sortDescending,
+        string? album = null, string? genre = null,
         CancellationToken ct = default);
 
     /// <summary>