Adds HolidayDatabase with 7 entries for 2026 (元旦/春节/清明/五一/
端午/中秋·国庆 + 2027 元旦 roll-over). WorkerStore.nextHoliday
computed returns the upcoming or currently-ongoing holiday with
days-until. WeekendView gains a tomato-tinted card under the
weekend hero showing "下个法定假 国庆 · 放 8 天 · X 天后" — or
"假期中" + 🎉 when the user opens the panel during the window.
Dates are estimated from typical State Council patterns; the file
header carries a TODO to verify against the official announcement
each year.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
