Add Stripe integration: webhook controller, service, sync command, Connect account

- Create StripeService: webhook sync, signature verification, save secret to .env.local
- Create StripeWebhookController with signature verification (400 on invalid)
- Create stripe:sync command to auto-create webhook endpoint via Stripe API
- Webhook listens to all events (configurable later)
- Save webhook secret automatically to .env.local on creation
- Add stripeAccountId field to User entity for Stripe Connect + migration
- Tests: StripeServiceTest (5), StripeWebhookControllerTest (2), StripeSyncCommandTest (1), UserTest updated

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

tests/Command/StripeSyncCommandTest.php

@@ -0,0 +1,19 @@
+<?php
+
+namespace App\Tests\Command;
+
+use App\Command\StripeSyncCommand;
+use App\Service\StripeService;
+use PHPUnit\Framework\TestCase;
+
+class StripeSyncCommandTest extends TestCase
+{
+    public function testCommandIsConfigured(): void
+    {
+        $stripeService = $this->createMock(StripeService::class);
+        $command = new StripeSyncCommand($stripeService);
+
+        self::assertSame('stripe:sync', $command->getName());
+        self::assertSame('Create or update the Stripe webhook endpoint', $command->getDescription());
+    }
+}