feat: Add event association to purchases; implement event relationship in models, update migration, and enhance tests

database/migrations/2026_08_04_000100_add_event_id_to_compras_table.php

@@ -0,0 +1,26 @@
+<?php
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\Schema;
+
+return new class extends Migration
+{
+    public function up(): void
+    {
+        Schema::table('compras', function (Blueprint $table): void {
+            $table->foreignId('event_id')
+                ->nullable()
+                ->after('tenant_codigo')
+                ->constrained('events')
+                ->nullOnDelete();
+        });
+    }
+
+    public function down(): void
+    {
+        Schema::table('compras', function (Blueprint $table): void {
+            $table->dropConstrainedForeignId('event_id');
+        });
+    }
+};