feat: redesign Android app with animations, charts, profile, and registration

- Register screen with validation (username, email, password, confirm)
- Profile screen with email editing and password change
- User greeting on dashboard showing logged-in username
- 401 auto-logout via SessionManager + AuthInterceptor
- MetricsChart with Canvas line graphs (CPU, RAM, Disk)
- Animated StatCard with counters and icons
- ServerCard with progress bars, pulsating status dot, dynamic elevation
- Shimmer loading placeholders
- Dark mode support with Material3
- Navigation transitions (slide + fade)
- New server rack launcher icon
- Splash screen
- Backend API: register, profile (GET/PUT) endpoints

views/layouts/main.php

@@ -76,6 +76,14 @@
                         </a>
                     </li>
                     <?php endif; ?>
+                    <li class="nav-divider"></li>
+                    <li class="nav-section">Mobile</li>
+                    <li class="nav-item">
+                        <a href="/sysadmin.apk" class="nav-link" download>
+                            <i class="fas fa-download"></i>
+                            <span>Download APK</span>
+                        </a>
+                    </li>
                 </ul>
             </nav>
             <div class="sidebar-footer">