fix(web,core): rebase remote promote-all onto series master delta

[tyler-dane]

Summary

Signed-in recurrence promote (scope: "all" after a middle-occurrence SHIFT+ARROW nudge) was forwarding the occurrence’s absolute schedule as the series master DTSTART. Local IndexedDB already rebases via shiftSeriesScheduleByOccurrenceEdit; remote did not.

• Extracted shared shiftSeriesScheduleByOccurrenceEdit into @core; local replaceSeries imports it
• Remote replace path rebases occurrence-absolute schedules onto a pre-optimistic series master snapshot when scope === "all"
• RemoteEventRepository skips IndexedDB fallback for occurrence + scope-all (avoids double-applying the delta)
• thisAndFollowing keeps absolute remainder DTSTART; local source unchanged

Simplicity

Collapsed all-day delta math onto dayjs.diff(..., "day") and shared promote/assert test helpers. Left resolveRemoteReplaceSchedule as a named helper — it documents the remote vs local ownership split.

Automated validation

• Unit: remote promote "all" middle timed + all-day → repository schedule is master+delta
• Unit: remote promote thisAndFollowing keeps absolute schedule
• Unit: remote scope-all + rules edit still rebases from pre-optimistic master snapshot
• Unit: local promote still sends absolute schedule (IndexedDB applies delta once)
• Unit: remote replace does not fall back to local for occurrence scope-all when backend is down
• Regression: local replaceSeries / nudge→promote suite green
• Signed-in browser not exercised here (auth/Google not provisioned); remote path covered by mutation + repository unit tests

Independent review

Fresh read-only review found three medium issues; all fixed in follow-up commits:

1. Remote→local fallback double-applied the delta → skip fallback for occurrence scope-all
2. Missing master soft-fails to absolute (by design; sync usually back-fills masters)
3. Optimistic rules edits could pollute cached master before rebase → snapshot master schedule onto mutation variables before onMutate

Test plan

• bun run test:core -- packages/core/src/util/event/shift-series-schedule-by-occurrence-edit.test.ts
• bun run test:web -- packages/web/src/events/mutations/useEventMutations.test.tsx packages/web/src/events/repositories/local.event.repository.test.ts packages/web/src/events/repositories/remote.event.repository.test.ts
• bun run type-check
• bun run lint