Add Roles/MQTT-settings/Backup pages, AdminLTE demo shells, and a separate mobile design system

Backend: real endpoints for role-permission overview, MQTT broker settings
(with live reachability check), and SQLite backup download/restore (new
system.manage permission, super-admin only; restore validates the SQLite
file header and keeps a pre-restore safety copy).

Desktop frontend: Roles (read-only permissions view), MQTT Settings,
Backup & Restore wired to those endpoints; plus static AdminLTE-matching
shells for Profile, Settings (embeds the real 2FA flow in its Security
tab), Invoice, Calendar (FullCalendar), Chat, File Manager, and Projects.

Mobile frontend: new frontend/src/styles/mobile.css, a from-scratch design
system (purple theme, cards, slide-out sidebar, bottom tab bar) scoped
entirely under a .mob-app root and mob- prefixed classes so it can never
collide with the desktop Bootstrap/AdminLTE styling. Rebuilt TopBar/
BottomNav, added a new SlideOutNav, and reskinned the Dashboard and Users
pages to it with real data.

backend/app/Http/Resources/RoleResource.php

@@ -14,6 +14,7 @@ class RoleResource extends JsonResource
     {
         return [
             'name' => $this->name,
+            'permissions' => $this->whenLoaded('permissions', fn () => $this->permissions->pluck('name')),
         ];
     }
 }