feat: complete Epic 0 — foundation migration & infrastructure setup

Stories 0.2-0.5: rename folders→declarations (backend+frontend), configure
Redis for cache/queue/sessions, add foundation database migrations
(permissions, archived_at), replace DeclarationStatus enum with architecture
lifecycle values, create DeclarationObserver for status transition validation
and auto-archive, fix controller status transitions to respect observer rules.

93 tests pass (240 assertions).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app/Notifications/DeclarationMentionNotification.php

@@ -0,0 +1,56 @@
+<?php
+
+namespace App\Notifications;
+
+use App\Models\Declaration;
+use App\Models\User;
+use Illuminate\Bus\Queueable;
+use Illuminate\Contracts\Queue\ShouldQueue;
+use Illuminate\Notifications\Messages\MailMessage;
+use Illuminate\Notifications\Notification;
+
+class DeclarationMentionNotification extends Notification implements ShouldQueue
+{
+    use Queueable;
+
+    public function __construct(
+        public Declaration $declaration,
+        public User $mentionedBy,
+        public string $message,
+    ) {}
+
+    /**
+     * @return array<string>
+     */
+    public function via(object $notifiable): array
+    {
+        return ['database', 'mail'];
+    }
+
+    /**
+     * @return array<string, mixed>
+     */
+    public function toDatabase(object $notifiable): array
+    {
+        return [
+            'declaration_id' => $this->declaration->id,
+            'declaration_title' => $this->declaration->title,
+            'mentioned_by_id' => $this->mentionedBy->id,
+            'mentioned_by_name' => $this->mentionedBy->name,
+            'message' => $this->message,
+            'url' => route('declarations.show', $this->declaration),
+        ];
+    }
+
+    public function toMail(object $notifiable): MailMessage
+    {
+        return (new MailMessage)
+            ->subject('Vous avez été mentionné - '.$this->declaration->title)
+            ->markdown('emails.declaration-mention', [
+                'declarationTitle' => $this->declaration->title,
+                'mentionedByName' => $this->mentionedBy->name,
+                'message' => $this->message,
+                'url' => route('declarations.show', $this->declaration),
+            ]);
+    }
+}