Move to JPA from hbm.xml, remove genericdao, update spring wiring (#136)

- Replaced the legacy Hibernate XML mappings with annotation-based JPA entities and moved date fields to Instant across the attendance domain model, adding the necessary relationship metadata and last-modified tracking.
- Refactored AttendanceDao and its implementation to drop GenericDAO, rely on the shared SessionFactory, and use the JPA Criteria API plus merge/Instant-aware queries and updates instead of named queries.
- Updated Spring wiring to enable @transactional on the service layer, inject the DAO directly, and introduce an AttendanceStatCalcService interface plus TransactionTemplate so the stats job can manage batch updates in explicit transactions.
- Adjusted stat-calculation and logic classes to operate on the new entity shape (including Instant sync times), and reworked the cron job to mark batches and calculate per site within dedicated transactions.
- Upgraded the Wicket stack to 9.21.0 and changed the tool UI to convert between Instant and Date, fix the breadcrumbs markup error, and ensure interactive links (e.g., in StudentView) bind safely without JavaScript fallbacks.
- Added lightweight unit tests covering model defaults/validation and the new stats helper to give coverage for the refactored code paths.

Author: ottenhoff