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

android/build.gradle.kts

@@ -0,0 +1,5 @@
+plugins {
+    id("com.android.application") version "9.2.1" apply false
+    id("org.jetbrains.kotlin.plugin.compose") version "2.3.21" apply false
+    id("org.jetbrains.kotlin.plugin.serialization") version "2.3.21" apply false
+}