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/app/proguard-rules.pro

@@ -0,0 +1,5 @@
+# Project-wide ProGuard rules
+-keepattributes Signature
+-keepattributes *Annotation*
+-keep class kotlinx.serialization.** { *; }
+-keepclassmembers class com.devlab.app.data.model.** { *; }