Phase 9E (Backbone): Stripe-Produkt-Sync und Webhook-Verarbeitung mit STR-Spiegelung

- billing:sync-stripe-plans: legt die Tarife als Netto-Produkte/Preise
  (tax_behavior exclusive, EUR) in Stripe an und pflegt die IDs zurueck
  nach plans; idempotent, --dry-run. Gegen Stripe Test-Mode ausgefuehrt —
  alle 4 Tiers verknuepft.
- ProcessStripeWebhook (Listener auf Cashier WebhookReceived):
  - invoice.payment_succeeded -> Spiegelung in den lokalen STR-Kreis
    (fortlaufende Nummer via InvoiceNumberGenerator, Adress-Snapshot
    bevorzugt aus dem Stripe-Payload inkl. lokaler USt-ID, Status paid,
    idempotent gegen doppelte Zustellung)
  - checkout.session.completed -> markiert den referenzierten
    single_purchases-Datensatz als bezahlt (Metadata single_purchase_id)
- CASHIER_CURRENCY=eur (+ Locale de_DE); Cashier-Webhook-Route aktiv
- Doku: Billing-Referenz §7 + Phase-9-Plan (9E-Backbone) aktualisiert

Offen fuer 9E-Rest: Checkout-Flows (Abo + Einmalkauf), Webhook-Endpoint
im Stripe-Dashboard + STRIPE_WEBHOOK_SECRET, Slot-Logik auf
Plan-Kontingent (fachliche Frage: Grandfathered = unbegrenzt?).

Tests: StripeWebhookProcessingTest (7, inkl. Event-Wiring).
Suite: 497 passed, 4 skipped. Pint clean.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

tests/Feature/Billing/StripeWebhookProcessingTest.php

@@ -0,0 +1,143 @@
+<?php
+
+use App\Enums\InvoiceStatus;
+use App\Enums\SinglePurchaseStatus;
+use App\Listeners\ProcessStripeWebhook;
+use App\Models\BillingAddress;
+use App\Models\Invoice;
+use App\Models\SinglePurchase;
+use App\Models\User;
+use Illuminate\Support\Facades\Event;
+use Laravel\Cashier\Events\WebhookReceived;
+
+function stripeInvoicePayload(User $user, array $overrides = []): array
+{
+    return [
+        'type' => 'invoice.payment_succeeded',
+        'data' => [
+            'object' => array_replace_recursive([
+                'id' => 'in_test_123',
+                'customer' => $user->stripe_id,
+                'subtotal' => 4900,
+                'tax' => 931,
+                'total' => 5831,
+                'currency' => 'eur',
+                'customer_name' => 'Alpha GmbH',
+                'customer_address' => [
+                    'line1' => 'Beispielweg 1',
+                    'line2' => null,
+                    'postal_code' => '10115',
+                    'city' => 'Berlin',
+                    'country' => 'DE',
+                ],
+            ], $overrides),
+        ],
+    ];
+}
+
+test('a paid stripe invoice is mirrored into the STR circle', function () {
+    $user = User::factory()->create(['stripe_id' => 'cus_test_1']);
+
+    app(ProcessStripeWebhook::class)->handle(new WebhookReceived(stripeInvoicePayload($user)));
+
+    $invoice = Invoice::sole();
+    expect($invoice->number)->toBe('STR-00001');
+    expect($invoice->user_id)->toBe($user->id);
+    expect($invoice->status)->toBe(InvoiceStatus::Paid);
+    expect($invoice->amount_cents)->toBe(4900);
+    expect($invoice->tax_cents)->toBe(931);
+    expect($invoice->total_cents)->toBe(5831);
+    expect($invoice->stripe_invoice_id)->toBe('in_test_123');
+    expect($invoice->invoiceBillingAddress->city)->toBe('Berlin');
+    expect($invoice->invoiceBillingAddress->name)->toBe('Alpha GmbH');
+});
+
+test('duplicate webhook deliveries do not create a second invoice', function () {
+    $user = User::factory()->create(['stripe_id' => 'cus_test_1']);
+    $listener = app(ProcessStripeWebhook::class);
+
+    $listener->handle(new WebhookReceived(stripeInvoicePayload($user)));
+    $listener->handle(new WebhookReceived(stripeInvoicePayload($user)));
+
+    expect(Invoice::count())->toBe(1);
+});
+
+test('the snapshot falls back to the local billing address including vat id', function () {
+    $user = User::factory()->create(['stripe_id' => 'cus_test_1']);
+    BillingAddress::factory()->create([
+        'user_id' => $user->id,
+        'name' => 'Lokal GmbH',
+        'country_code' => 'AT',
+        'vat_id' => 'ATU12345678',
+    ]);
+
+    app(ProcessStripeWebhook::class)->handle(new WebhookReceived(stripeInvoicePayload($user, [
+        'customer_name' => null,
+        'customer_address' => null,
+    ])));
+
+    $snapshot = Invoice::sole()->invoiceBillingAddress;
+    expect($snapshot->name)->toBe('Lokal GmbH');
+    expect($snapshot->country_code)->toBe('AT');
+    expect($snapshot->vat_id)->toBe('ATU12345678');
+});
+
+test('an unknown stripe customer is skipped without an invoice', function () {
+    User::factory()->create(['stripe_id' => 'cus_other']);
+
+    app(ProcessStripeWebhook::class)->handle(new WebhookReceived(stripeInvoicePayload(
+        new User(['name' => 'Fremd']),
+        ['customer' => 'cus_unknown'],
+    )));
+
+    expect(Invoice::count())->toBe(0);
+});
+
+test('checkout completion marks the referenced single purchase as paid', function () {
+    $purchase = SinglePurchase::factory()->create();
+
+    app(ProcessStripeWebhook::class)->handle(new WebhookReceived([
+        'type' => 'checkout.session.completed',
+        'data' => [
+            'object' => [
+                'id' => 'cs_test_1',
+                'payment_intent' => 'pi_test_1',
+                'metadata' => ['single_purchase_id' => (string) $purchase->id],
+            ],
+        ],
+    ]));
+
+    $fresh = $purchase->fresh();
+    expect($fresh->status)->toBe(SinglePurchaseStatus::Paid);
+    expect($fresh->paid_at)->not->toBeNull();
+    expect($fresh->stripe_checkout_session_id)->toBe('cs_test_1');
+    expect($fresh->stripe_payment_intent_id)->toBe('pi_test_1');
+});
+
+test('an already paid purchase is not touched again', function () {
+    $purchase = SinglePurchase::factory()->paid()->create([
+        'stripe_payment_intent_id' => 'pi_original',
+    ]);
+
+    app(ProcessStripeWebhook::class)->handle(new WebhookReceived([
+        'type' => 'checkout.session.completed',
+        'data' => [
+            'object' => [
+                'id' => 'cs_test_2',
+                'payment_intent' => 'pi_new',
+                'metadata' => ['single_purchase_id' => (string) $purchase->id],
+            ],
+        ],
+    ]));
+
+    expect($purchase->fresh()->stripe_payment_intent_id)->toBe('pi_original');
+});
+
+test('the listener is wired to the cashier webhook event', function () {
+    Event::fake();
+
+    Event::assertListening(
+        WebhookReceived::class,
+        ProcessStripeWebhook::class,
+    );
+});