- API GET /api/logs now accepts from_ts / to_ts (unix epoch, half-open
[from, to)) so callers can scope by arbitrary time range.
- API DELETE /api/logs added. Same from_ts / to_ts semantics. No params
= wipe everything and reset the AUTOINCREMENT counter.
- Dashboard Logs page: date picker that scopes both the view and the
delete button to the selected day in the user's local timezone. The
clear button is red and confirms before deleting; label switches
between "전체 로그 초기화" and "<날짜> 하루치 삭제".