Around New Year the empty-rota guard keeps the old year's cached rows
while resolveRange has already moved to the new year's tab, so an
auto-assignment could write an old-tab row index onto the new tab.
Stamp each DutyWeek with the tab it was fetched from and prefer it when
building the assignment range (clock fallback for pre-upgrade caches).
Also: widen the default fetch range to A1:G200 so a full year of rows
plus roster can't be silently truncated, add -race/golangci-lint/
govulncheck gates to CI (container pinned to 1.26.4-alpine), and add
.env.example documenting every configuration variable.
Kamil 'Kamaś' Bruchal
kamash