test: add MaterialDetailViewModel unit tests (IOS-INFO-035)
- 20 tests covering initial state + helpers
- Initial state: isLoading, aiStatus, itemCount, quizCount, isMarkedRead,
readingSeconds, readingStatus, knowledgeBaseId, materialId
- init without materialId defaults to nil
- statusLabel: completed/in_progress/unknown/nil → Chinese labels
- formatSeconds: seconds(0/30/59), minutes(60/3599), hours(3600/3660/7200)
- Edge: nil materialId skips progress fetch
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
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