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/Mail/DeclarationTextMessageMail.php

@@ -0,0 +1,55 @@
+<?php
+
+namespace App\Mail;
+
+use App\Models\Declaration;
+use Illuminate\Bus\Queueable;
+use Illuminate\Mail\Mailable;
+use Illuminate\Mail\Mailables\Content;
+use Illuminate\Mail\Mailables\Envelope;
+use Illuminate\Queue\SerializesModels;
+
+class DeclarationTextMessageMail extends Mailable
+{
+    use Queueable, SerializesModels;
+
+    /**
+     * Create a new message instance.
+     *
+     * @param  string|null  $token  When set, recipient is client (use token-based URL). When null, recipient is comptable (use declarations.show).
+     */
+    public function __construct(
+        public Declaration $declaration,
+        public string $body,
+        public ?string $token = null
+    ) {}
+
+    /**
+     * Get the message envelope.
+     */
+    public function envelope(): Envelope
+    {
+        return new Envelope(
+            subject: 'Nouveau message - '.$this->declaration->title,
+        );
+    }
+
+    /**
+     * Get the message content definition.
+     */
+    public function content(): Content
+    {
+        $messagesUrl = $this->token
+            ? route('client.upload', ['token' => $this->token])
+            : route('declarations.show', ['declaration' => $this->declaration]).'?tab=messages';
+
+        return new Content(
+            markdown: 'emails.declaration-text-message',
+            with: [
+                'declarationTitle' => $this->declaration->title,
+                'body' => $this->body,
+                'messagesUrl' => $messagesUrl,
+            ]
+        );
+    }
+}