feat(api): organisation email branding and shared mail layout

- Add email branding columns to organisations table (logo, color, reply-to, sender name, footer)
- Create MailBrandingService for resolving per-org branding with defaults
- Create CrewliMailable abstract base class with branded from/reply-to
- Create shared Blade layout (mail.layouts.crewli) with inline CSS
- Refactor Registration*Mail and InvitationMail to extend CrewliMailable
- Add config/crewli.php for platform-wide defaults (portal_url, app_url, logo)
- Add dev-only /mail-preview/{type} route for browser email previewing
- Update Organisation model, resource, and form requests with branding fields

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

api/app/Mail/InvitationMail.php

@@ -5,21 +5,18 @@ declare(strict_types=1);
 namespace App\Mail;
 
 use App\Models\UserInvitation;
-use Illuminate\Bus\Queueable;
-use Illuminate\Contracts\Queue\ShouldQueue;
-use Illuminate\Mail\Mailable;
 use Illuminate\Mail\Mailables\Content;
 use Illuminate\Mail\Mailables\Envelope;
-use Illuminate\Queue\SerializesModels;
 
-final class InvitationMail extends Mailable implements ShouldQueue
+final class InvitationMail extends CrewliMailable
 {
-    use Queueable;
-    use SerializesModels;
+    public UserInvitation $invitation;
 
-    public function __construct(
-        public readonly UserInvitation $invitation,
-    ) {}
+    public function __construct(UserInvitation $invitation)
+    {
+        parent::__construct($invitation->organisation);
+        $this->invitation = $invitation;
+    }
 
     public function envelope(): Envelope
     {
@@ -30,11 +27,12 @@ final class InvitationMail extends Mailable implements ShouldQueue
 
     public function content(): Content
     {
+        $this->buildBranding();
+
         return new Content(
-            markdown: 'emails.invitation',
+            view: 'mail.invitation',
             with: [
-                'acceptUrl' => config('app.frontend_app_url') . '/invitations/' . $this->invitation->token . '/accept',
-                'organisationName' => $this->invitation->organisation->name,
+                'acceptUrl' => config('crewli.app_url') . '/invitations/' . $this->invitation->token . '/accept',
                 'inviterName' => $this->invitation->invitedBy?->name ?? 'Een beheerder',
                 'role' => $this->invitation->role,
                 'expiresAt' => $this->invitation->expires_at,