fix: nullable type for jellyfinMediaId(4k) (#702)

The jellyfinMediaId(4k) properties were inferred as string | undefined, causing them to be set to
undefined when assigning null. This prevented the media from being saved correctly to the SQLite
database, as it doesn't accept undefined values. This resolves the availabilitySync job issue where
the "play on" button wasn't being removed for all media server types.

fix #668

server/lib/scanners/jellyfin/index.ts

@@ -168,9 +168,9 @@ class JellyfinScanner {
           newMedia.jellyfinMediaId =
             hasOtherResolution || (!this.enable4kMovie && has4k)
               ? metadata.Id
-              : undefined;
+              : null;
           newMedia.jellyfinMediaId4k =
-            has4k && this.enable4kMovie ? metadata.Id : undefined;
+            has4k && this.enable4kMovie ? metadata.Id : null;
           await mediaRepository.save(newMedia);
           this.log(`Saved ${metadata.Name}`);
         }
@@ -461,9 +461,9 @@ class JellyfinScanner {
               tmdbId: tvShow.id,
               tvdbId: tvShow.external_ids.tvdb_id,
               mediaAddedAt: new Date(metadata.DateCreated ?? ''),
-              jellyfinMediaId: isAllStandardSeasons ? Id : undefined,
+              jellyfinMediaId: isAllStandardSeasons ? Id : null,
               jellyfinMediaId4k:
-                isAll4kSeasons && this.enable4kShow ? Id : undefined,
+                isAll4kSeasons && this.enable4kShow ? Id : null,
               status: isAllStandardSeasons
                 ? MediaStatus.AVAILABLE
                 : newSeasons.some(