Set up pytest with Home Assistant support and created 6 tests for
midnight-crossing period logic (5 unit tests + 1 integration test).
Added pytest configuration, test dependencies, test runner script
(./scripts/test), and comprehensive tests for group_periods_by_day()
and midnight turnover consistency.
All tests pass in 0.12s.
Impact: Provides regression testing for midnight-crossing period bugs.
Tests validate periods remain visible across midnight turnover.