add element youtube url

backend/database/migrations/2026_05_24_000001_elements_table.php

@@ -15,6 +15,7 @@ return new class extends Migration
             $table->text('description')->default('');
             $table->text('rich_text')->default('');
             $table->string('pdf_path')->nullable();
+            $table->string('youtube_url')->nullable();
             $table->foreignId('parent_element_id')
                 ->nullable()
                 ->constrained('elements');