feat(120): alert component unification

Phase 120 - Plan 01:
- Reusable PHP alert component (resources/views/components/alert.php)
  with inline SVG icon per type, optional dismiss button.
- Missing .alert--info SCSS variant added (#eff6ff/#bfdbfe/#1e3a8a) -
  fixes black-on-white alert after Fakturownia test connection.
- Flash::push(type, message) + Flash::all() with BC for set/get;
  legacy key heuristic (error/.save/warning -> typed entries).
- Central flash renderer in 3 layouts (app/auth/public) iterating
  Flash::all() through component (.alerts-stack wrap).
- Vanilla JS alert-dismiss.js with idempotent guard and delegated
  click handler on [data-alert-dismiss].
- 36 views migrated off inline <div class="alert alert--TYPE">;
  .flash--error/success removed from views (orders/show, shipments/prepare).
- SCSS rebuilt: public/assets/css/{app,login}.css.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

resources/views/orders/receipt-create.php

@@ -22,7 +22,9 @@ $hasExistingReceipts = $existingReceiptsList !== [];
   </div>
 
   <?php if ($hasExistingReceipts): ?>
-    <div class="alert alert--warning mt-12">
+    <?php
+      ob_start();
+    ?>
       <strong>Uwaga!</strong> Do tego zamówienia wystawiono już <?= $e((string) count($existingReceiptsList)) ?> paragon(ów):
       <ul class="mt-4">
         <?php foreach ($existingReceiptsList as $er): ?>
@@ -35,7 +37,10 @@ $hasExistingReceipts = $existingReceiptsList !== [];
           </li>
         <?php endforeach; ?>
       </ul>
-    </div>
+    <?php
+      $existingReceiptsHtml = ob_get_clean();
+    ?>
+    <div class="mt-12"><?php $type='warning'; $messageHtml = $existingReceiptsHtml; $dismissible=true; include dirname(__DIR__) . '/components/alert.php'; unset($messageHtml); ?></div>
   <?php endif; ?>
 
   <form id="receipt-create-form" method="post" action="/orders/<?= $e((string) $orderIdVal) ?>/receipt/store" class="mt-16">