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/Http/Requests/Api/V1/UpdateOrganisationRequest.php

@@ -25,6 +25,11 @@ final class UpdateOrganisationRequest extends FormRequest
             ],
             'billing_status' => ['sometimes', 'string', 'in:active,trial,suspended'],
             'settings' => ['sometimes', 'array'],
+            'email_logo_url' => ['nullable', 'url', 'max:500'],
+            'email_primary_color' => ['nullable', 'string', 'regex:/^#[0-9A-Fa-f]{6}$/'],
+            'email_reply_to' => ['nullable', 'email'],
+            'email_sender_name' => ['nullable', 'string', 'max:100'],
+            'email_footer_text' => ['nullable', 'string', 'max:2000'],
         ];
     }
 }