feat(chart-of-accounts): allow null unit_id for matriz plan accounts

Plano de contas da matriz (franqueador) não pertence a uma unidade.

database/migrations/2026_06_18_000003_make_unit_id_nullable_on_financial_plan_accounts.php

@@ -0,0 +1,23 @@
+<?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('financial_plan_accounts', function (Blueprint $table) {
+            // Plano de contas da matriz (franqueador) não pertence a uma unidade.
+            $table->foreignId('unit_id')->nullable()->change();
+        });
+    }
+
+    public function down(): void
+    {
+        Schema::table('financial_plan_accounts', function (Blueprint $table) {
+            $table->foreignId('unit_id')->nullable(false)->change();
+        });
+    }
+};