refactor(study-options): add StudyOptionsViewModel with state management

- Extract business logic from StudyOptionsFragment into a dedicated
ViewModel.
- Introduces DeckStudyData, StudyOptionsState sealed interface,
and moves collection queries and deck operations (rebuild, empty, unbury)
into the ViewModel.
- refactor(study-options): wire StudyOptionsFragment to use ViewModel
- test(study-options): add unit tests for StudyOptionsViewModel

Author: criticalAY