Parse each job's schedule once on load (resetNextRuns) and on edit
(RefreshSchedule) via the new parseJobSchedule helper, caching the
result in a map[int]domain.Schedule keyed by job ID. prepareNextRun
now looks up the cached Schedule instead of re-parsing the string on
every call. Remove the nextRunTime wrapper that did the per-call
parsing. Drop the three scheduler_test.go tests that duplicated
coverage already in domain/schedule_test.go.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
