feat: admin app version mgmt + notification system

- New tables: app_config, notifications
- Admin views: App Version editor, Notification sender
- API: GET /api/notifications, POST /api/notifications/:id/read, POST /api/notifications/read-all
- App version now stored in DB, editable by super admin
- Notifications: send to all users or specific user
- Android notification models + API client
- Sidebar: App Version + Notifications links for super_admin

views/layouts/main.php

@@ -66,6 +66,18 @@
                             <span>Security</span>
                         </a>
                     </li>
+                    <li class="nav-item">
+                        <a href="/admin/app-version" class="nav-link <?= str_starts_with($_SERVER['REQUEST_URI'] ?? '', '/admin/app-version') ? 'active' : '' ?>">
+                            <i class="fas fa-mobile-alt"></i>
+                            <span>App Version</span>
+                        </a>
+                    </li>
+                    <li class="nav-item">
+                        <a href="/admin/notifications" class="nav-link <?= str_starts_with($_SERVER['REQUEST_URI'] ?? '', '/admin/notifications') ? 'active' : '' ?>">
+                            <i class="fas fa-bell"></i>
+                            <span>Notifications</span>
+                        </a>
+                    </li>
                     <?php elseif (is_admin()): ?>
                     <li class="nav-divider"></li>
                     <li class="nav-section">Administration</li>