feat: add search/album/genre filtering and /albums + /genres browse pages

DeepDrftModels/DTOs/TrackFilter.cs

@@ -0,0 +1,27 @@
+namespace DeepDrftModels.DTOs;
+
+/// <summary>
+/// Cross-project track filter contract. Threaded alongside (never inside) the external
+/// <c>PagingParameters&lt;T&gt;</c>, which cannot carry a where-clause. An instance with all
+/// properties null is equivalent to no filter — see <c>TrackFilter.IsEmpty</c>.
+/// </summary>
+public class TrackFilter
+{
+    /// <summary>Free-text, case-insensitive LIKE across TrackName, Artist, and Album.</summary>
+    public string? SearchText { get; set; }
+
+    /// <summary>Exact album match.</summary>
+    public string? Album { get; set; }
+
+    /// <summary>Exact genre match.</summary>
+    public string? Genre { get; set; }
+
+    /// <summary>
+    /// True when no predicate is set. An empty filter must produce identical results to a null
+    /// filter, so callers collapse it to null before querying.
+    /// </summary>
+    public bool IsEmpty =>
+        string.IsNullOrWhiteSpace(SearchText)
+        && string.IsNullOrWhiteSpace(Album)
+        && string.IsNullOrWhiteSpace(Genre);
+}