Extend the time-of-day condition from a bare server-local HH:MM window to a real
schedule: pick which weekdays it is active (0=Mon..6=Sun, empty = every day) and
an optional IANA timezone (empty = server local). Closes the parity gap where
even a $5 WLED chip has weekday timers.
- Overnight windows (start > end) count toward the day they START on, so the
after-midnight tail is matched against the previous weekday.
- Timezones are resolved via zoneinfo, cached, and fall back to server-local
with a one-time warning on an invalid name (the ~1Hz tick never log-spams).
- Backward compatible: new fields default to all-days / server-local, so
existing automations are unchanged (no migration).
- Frontend: weekday chips + timezone input on the rule editor, day/timezone in
the rule summary, styles + i18n (en/ru/zh).
10 unit tests (weekday filter, overnight start-day semantics, tz fallback,
round-trip, invalid-day filtering); full suite green (1936 passed).
(Geographic sunrise/sunset triggers are a natural follow-up — the daylight
value source already has the solar math to reuse.)
