feat(infrastructure): implement SQLite persistence layer for calendar domain

Add infrastructure layer with SQLite repositories for
calendars, events, and recurring events. Implements the repository
pattern with proper domain/infrastructure separation.

- Add CalendarModel, EventModel, RecurrenceModel, and RecurrenceExceptionModel
  for database persistence
- Implement SqliteCalendarRepository with CRUD operations
- Implement SqliteEventRepository with calendar filtering and time range queries
- Implement SqliteRecurringEventRepository with exception handling and transactions
- Add bidirectional mappers between domain entities and persistence models
- Use sqlx query_as for type-safe database queries with FromRow derivation
- Support upsert operations for all entities using ON CONFLICT clauses

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