- tests/conftest.py: put repo root on sys.path so `import src...` resolves
under pytest regardless of invocation directory.
- test_matrix_formatting.py: lock in HTML formatted_body + plain-text fallback,
URL linkification, HTML escaping, and send_alert field rendering.
- test_station_persistence.py: cover default-load, save/reload round-trip
(incl. Thai text), runtime-file precedence, and atomic-write cleanup.
These are real assert-based tests (unlike the existing print-style scripts) so
CI can gate on them. 13 tests, all passing.
