ui: enhance authentication screen with animations and improved layout

- Implement `AnimatedContent` for smooth transitions between different authentication states (LoggedOut, DevicePrompt, Pending, LoggedIn, Error).
- Add scale and fade animations for the app icon and status indicators using `animateFloatAsState` and `AnimatedVisibility`.
- Refactor state-specific UI into dedicated private composables (`StateLoggedOut`, `StateDevicePrompt`, `StatePending`, `StateLoggedIn`, `StateError`) for better maintainability.
- Enhance the `StateDevicePrompt` with an animated countdown progress bar, urgent color states for expiring codes, and improved typography.
- Modernize the UI using `ElevatedCard`, `FilledTonalButton`, and standardized spacing/padding across all states.
- Improve visual feedback for the "copy code" action and polling status with icon animations and a `CircularProgressIndicator`.
- Update previews to cover more authentication scenarios including logged-in and error states with recovery hints.

Author: rainxchzed