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/FolderTextMessageMail.php

@@ -1,55 +0,0 @@
-<?php
-
-namespace App\Mail;
-
-use App\Models\Folder;
-use Illuminate\Bus\Queueable;
-use Illuminate\Mail\Mailable;
-use Illuminate\Mail\Mailables\Content;
-use Illuminate\Mail\Mailables\Envelope;
-use Illuminate\Queue\SerializesModels;
-
-class FolderTextMessageMail 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 folders.show).
-     */
-    public function __construct(
-        public Folder $folder,
-        public string $body,
-        public ?string $token = null
-    ) {}
-
-    /**
-     * Get the message envelope.
-     */
-    public function envelope(): Envelope
-    {
-        return new Envelope(
-            subject: 'Nouveau message - '.$this->folder->title,
-        );
-    }
-
-    /**
-     * Get the message content definition.
-     */
-    public function content(): Content
-    {
-        $messagesUrl = $this->token
-            ? route('client.upload', ['token' => $this->token])
-            : route('folders.show', ['folder' => $this->folder]).'?tab=messages';
-
-        return new Content(
-            markdown: 'emails.folder-text-message',
-            with: [
-                'folderTitle' => $this->folder->title,
-                'body' => $this->body,
-                'messagesUrl' => $messagesUrl,
-            ]
-        );
-    }
-}