feat(api): browse all media kinds, grouped search, delete media-items (#141, #161)

- Extend /api/library/browse to episodes, music videos, songs, other videos,
  images and remote streams (new LibraryBrowseMediaType values + hydrators);
  add optional Subtitle to LibraryBrowseItemResponseModel for leaf-item context
- Add GET /api/search: grouped per-kind results reusing the browse query/shape;
  empty query -> 422
- Add DELETE /api/media-items: body { ids }, empty -> 422, success -> 204
- Tests: SearchController, MediaItemsController, security + OpenAPI contract entries
- Regenerate openapi v1.json + web v1.d.ts

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

ErsatzTV.Core/Api/LibraryBrowse/LibraryBrowseItemResponseModel.cs

@@ -19,4 +19,5 @@ public record LibraryBrowseItemResponseModel(
     int? SmartCollectionId,
     int? RerunCollectionId,
     int? MediaItemId,
-    int? PlaylistId);
+    int? PlaylistId,
+    string? Subtitle = null);

ErsatzTV.Core/Api/LibraryBrowse/LibraryBrowseMediaType.cs

@@ -11,5 +11,11 @@ public enum LibraryBrowseMediaType
     SmartCollection = 6,
     MultiCollection = 7,
     RerunCollection = 8,
-    Playlist = 9
+    Playlist = 9,
+    Episode = 10,
+    MusicVideo = 11,
+    Song = 12,
+    OtherVideo = 13,
+    Image = 14,
+    RemoteStream = 15
 }

ErsatzTV.Core/Api/Search/SearchResultGroupResponseModel.cs

@@ -0,0 +1,8 @@
+#nullable enable
+using ErsatzTV.Core.Api.LibraryBrowse;
+
+namespace ErsatzTV.Core.Api.Search;
+
+public record SearchResultGroupResponseModel(
+    int TotalCount,
+    List<LibraryBrowseItemResponseModel> Items);

ErsatzTV.Core/Api/Search/SearchResultsResponseModel.cs

@@ -0,0 +1,14 @@
+#nullable enable
+namespace ErsatzTV.Core.Api.Search;
+
+public record SearchResultsResponseModel(
+    SearchResultGroupResponseModel Movies,
+    SearchResultGroupResponseModel Shows,
+    SearchResultGroupResponseModel Seasons,
+    SearchResultGroupResponseModel Artists,
+    SearchResultGroupResponseModel Episodes,
+    SearchResultGroupResponseModel MusicVideos,
+    SearchResultGroupResponseModel Songs,
+    SearchResultGroupResponseModel OtherVideos,
+    SearchResultGroupResponseModel Images,
+    SearchResultGroupResponseModel RemoteStreams);