Enable EF Core SplitQuery for PostgreSQL provider

Configured QuerySplittingBehavior.SplitQuery in PostgresDatabaseProvider to optimize performance for queries with multiple Include() statements. This prevents cartesian explosion, eliminates EF Core warnings, and aligns with best practices for handling related collections in PostgreSQL.

src/Jellyfin.Database/Jellyfin.Database.Providers.Postgres/PostgresDatabaseProvider.cs

@@ -158,7 +158,11 @@ public sealed class PostgresDatabaseProvider : IJellyfinDatabaseProvider
         options
             .UseNpgsql(
                 connectionString,
-                npgsqlOptions => npgsqlOptions.MigrationsAssembly(GetType().Assembly.FullName))
+                npgsqlOptions =>
+                {
+                    npgsqlOptions.MigrationsAssembly(GetType().Assembly.FullName);
+                    npgsqlOptions.UseQuerySplittingBehavior(QuerySplittingBehavior.SplitQuery);
+                })
             .ConfigureWarnings(warnings =>
                 warnings.Ignore(Microsoft.EntityFrameworkCore.Diagnostics.RelationalEventId.PendingModelChangesWarning));