Integrate PartialTranscriptionRepository for crash recovery

Implement debounce using a Timer? _persistDebounce field: cancel and reset the timer on each PartialResult, fire the upsert only when the timer fires. Choose 300ms as the debounce interval (configurable via a const). Place the initial recovery check in an async init method called from the StateNotifier constructor body using Future.microtask(() async { ...

}) so it does not block provider instantiation. The abstract interface for PartialTranscriptionRepository (already hinted at in task-004) must have at minimum: Future findByFieldId(String fieldId), Future upsert(String fieldId, String text), Future deleteByFieldId(String fieldId). Ensure the DictationProcessing state (already defined in task-001) carries a partialTranscript field so the UI can display the recovered text and prompt the user to review or discard. The recovery flow (DictationProcessing on load) should be clearly distinguished from the normal DictationProcessing state (after stopDictation) — consider adding an isRecovery: bool flag to DictationProcessing if the distinction matters for UI treatment.

Unit tests using flutter_test with a fake PartialTranscriptionRepository (in-memory implementation for tests). Test cases: (1) on init with existing partial record → state is DictationProcessing with correct transcript text; (2) on init with no partial record → state is DictationIdle; (3) on init with repository error → state is DictationIdle (safe degradation); (4) PartialResult event triggers debounced upsert — verify upsert called after debounce interval using fake async; (5) DictationComplete → deleteByFieldId called; (6) cancelDictation() → deleteByFieldId called; (7) upsert error does not change state machine state; (8) concurrent partial emissions within debounce window result in exactly one upsert. Use fake_async package for debounce testing. Minimum 90% coverage on repository integration code paths.