Add-ons: Modal statt Toast bei fehlendem Credit-Guthaben

Scheiterte ein Boost- oder Nachweis-Kauf am Wallet-Guthaben, gab es nur
einen flüchtigen Toast ohne Weg zur Lösung. Jetzt öffnet sich ein Modal
mit Kosten, Guthaben und fehlender Differenz sowie einem Direktlink
"Credits aufladen" zur Wallet-Sektion der Buchungsseite (neuer
#credits-Anker).

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

tests/Feature/PressReleaseShowAddonsTest.php

@@ -83,6 +83,42 @@ test('buying a proof from the detail page unlocks the download', function () {
     expect($customer->fresh()->creditBalance())->toBe(7);
 });
 
+test('an add-on purchase without enough credits opens the shortfall modal with a topup link', function () {
+    /** @var TestCase $this */
+    ['customer' => $customer, 'pr' => $pr] = publishedGreenPrForOwner();
+    $this->wallet->credit($customer, 1);
+
+    $this->actingAs($customer);
+
+    LivewireVolt::test('customer.press-releases.show', ['id' => $pr->id])
+        ->call('buyProof')
+        ->assertSet('creditShortfall', [
+            'label' => 'Der Veröffentlichungsnachweis',
+            'required' => 3,
+            'available' => 1,
+        ])
+        ->assertSee('Nicht genügend Credits')
+        ->assertSee('Es fehlen 2 Credits.')
+        ->assertSee('Credits aufladen')
+        ->assertSee(route('me.bookings.index').'#credits', escape: false);
+
+    expect($customer->fresh()->creditBalance())->toBe(1); // nichts abgebucht
+});
+
+test('a boost without enough credits opens the shortfall modal instead of booking', function () {
+    /** @var TestCase $this */
+    ['customer' => $customer, 'pr' => $pr] = publishedGreenPrForOwner();
+
+    $this->actingAs($customer);
+
+    LivewireVolt::test('customer.press-releases.show', ['id' => $pr->id])
+        ->call('buyBoost', 7)
+        ->assertSet('creditShortfall.label', 'Der Boost')
+        ->assertSee('Nicht genügend Credits');
+
+    expect($pr->fresh()->isBoosted())->toBeFalse();
+});
+
 test('a non-green release cannot be boosted from the detail page', function () {
     /** @var TestCase $this */
     ['customer' => $customer, 'pr' => $pr] = publishedGreenPrForOwner();