new: send stock alert email when offer stock crosses threshold

When a purchase causes an offer's ``stock_current`` to drop to or below
its ``minimum_ondemand`` threshold, an email is sent to
``commande@jardinenvie.com`` using an editable mail template (Spatie
``MailTemplate``).

The check runs in ``OfferStocks::decreaseStock()`` after updating stock.
Only threshold-crossing events trigger the alert (not every low-stock
sale).  Failures are caught and logged to avoid disrupting the order
flow.

app/Mail/AlerteStock.php

@@ -0,0 +1,43 @@
+<?php
+
+namespace App\Mail;
+
+use App\Models\Core\Mail\MailTemplate;
+use Illuminate\Bus\Queueable;
+use Illuminate\Mail\Mailables\Address;
+use Illuminate\Mail\Mailables\Envelope;
+use Illuminate\Queue\SerializesModels;
+use Spatie\MailTemplates\TemplateMailable;
+
+class AlerteStock extends TemplateMailable
+{
+    use Queueable, SerializesModels;
+
+    public $subject;
+
+    public $article;
+
+    public $offre;
+
+    public $stock_restant;
+
+    public $seuil;
+
+    protected static $templateModelClass = MailTemplate::class;
+
+    public function __construct($offer)
+    {
+        $this->article = $offer->article->title ?? 'Article #'.$offer->article_id;
+        $this->offre = $offer->id;
+        $this->stock_restant = $offer->stock_current;
+        $this->seuil = $offer->minimum_ondemand;
+    }
+
+    public function envelope()
+    {
+        return new Envelope(
+            from: new Address('boutique@jardinenvie.com', 'Jardin\'en\'Vie'),
+            subject: $this->subject,
+        );
+    }
+}