feat: replace /archive with release-cardinal searchable browser (Phase 9 §8.H)

Retire the three-card overview for a search + medium + genre browser over all
releases. Adds q/genre filter params to the api/release paged read path,
mirroring the existing api/track/page TrackFilter pattern.

DeepDrftModels/DTOs/ReleaseFilter.cs

@@ -0,0 +1,25 @@
+namespace DeepDrftModels.DTOs;
+
+/// <summary>
+/// Cross-project release filter contract for the paged release read surface. Threaded alongside
+/// (never inside) the external <c>PagingParameters&lt;T&gt;</c>, which cannot carry a where-clause,
+/// and beside the medium filter (a separate enum param, not a free-text field). Mirrors
+/// <see cref="TrackFilter"/> for the release-cardinal browse path. An instance with all properties
+/// null is equivalent to no filter — see <see cref="IsEmpty"/>.
+/// </summary>
+public class ReleaseFilter
+{
+    /// <summary>Free-text, case-insensitive LIKE across the release Title and Artist.</summary>
+    public string? SearchText { 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(Genre);
+}