fix(home): resolve missing thumbnails for music videos and videos (#490)

Recently downloaded music videos and videos do not extract Thumb artwork
on the Jellyfin server by default anymore. On home screen rows using
ImageType.thumb (such as Continue Watching or plugin-generated sections),
they would fall back to parent artist/folder backdrop or thumbnail, or
render completely blank cards if those were missing.

This commit updates _resolveRowImageUrl and _resolveLandscapeImageUrl
in home_screen.dart to:
1. Fall back to the item's own Primary image for MusicVideo and Video
   types when Thumb artwork is missing, instead of falling back to
   parent backdrop/thumbnail.
2. Skip the parent backdrop image fallback logic for MusicVideo and Video
   types, ensuring their own Primary image takes precedence.

This aligns home screen resolving logic with the library browse screen.

Closes #271

Co-authored-by: mattsigal <mattsigal@users.noreply.github.com>

Author: mattsigal

lib/ui/screens/home/home_screen.dart

@@ -3618,14 +3618,16 @@ class _ContentRowsState extends State<_ContentRows>
         tag: item.backdropImageTags.first,
       );
     }
-    final parentId = item.parentBackdropItemId;
-    final parentTags = item.parentBackdropImageTags;
-    if (parentId != null && parentTags.isNotEmpty) {
-      return imageApi.getBackdropImageUrl(
-        parentId,
-        maxWidth: maxW,
-        tag: parentTags.first,
-      );
+    if (item.type != 'Video' && item.type != 'MusicVideo') {
+      final parentId = item.parentBackdropItemId;
+      final parentTags = item.parentBackdropImageTags;
+      if (parentId != null && parentTags.isNotEmpty) {
+        return imageApi.getBackdropImageUrl(
+          parentId,
+          maxWidth: maxW,
+          tag: parentTags.first,
+        );
+      }
     }
     return _resolvePrimaryImageUrl(item, imageApi, maxWidth: maxW);
   }
@@ -3845,16 +3847,16 @@ class _ContentRowsState extends State<_ContentRows>
     if (imageType == ImageType.thumb) {
       final maxW = (height * 16 / 9 * requestScale).toInt();
       final maxH = (height * requestScale).toInt();
-      if (!useSeriesThumbs) {
-        if (item.type == 'Episode') {
-          final episodePrimary = _resolvePrimaryImageUrl(
+      if (!useSeriesThumbs || item.type == 'Video' || item.type == 'MusicVideo') {
+        if (item.type == 'Episode' || item.type == 'Video' || item.type == 'MusicVideo') {
+          final videoPrimary = _resolvePrimaryImageUrl(
             item,
             imageApi,
             maxHeight: maxH,
             maxWidth: maxW,
           );
-          if (episodePrimary != null) {
-            return episodePrimary;
+          if (videoPrimary != null) {
+            return videoPrimary;
           }
         } else if (item.type == 'Series') {
           final latestEpId = item.rawData['LatestEpisodeId'] as String?;