Establish split score definition

database/migrations/2025_10_31_125143_create_split_score_definitions_table.php

@@ -15,7 +15,7 @@ return new class extends Migration
         Schema::create('split_score_definitions', function (Blueprint $table) {
             $table->id();
             $table->foreignIdFor(Audition::class)->constrained()->cascadeOnDelete()->cascadeOnUpdate();
-            $table->json('splits')->default('{}');
+            $table->json('splits')->nullable();
             $table->timestamps();
         });
     }