Two new endpoints under existing RequireAdmin middleware:
- GET /api/admin/scan/schedule — returns config + computed
next_scheduled_at (ISO 8601; null when mode='off')
- PATCH /api/admin/scan/schedule — validates per-mode required
fields, normalizes mode='off' to NULL the per-mode fields,
writes via UpdateScanSchedule, calls scheduler.Refresh(), returns
the updated record.
server.New + api.Mount gain a *library.Scheduler parameter; handlers
struct + Server struct gain the scheduler field. Test stubs
(server_test.go, library_test.go's Mount call) updated to pass nil.
Tests gated on MINSTREL_TEST_DATABASE_URL: GET default is mode=off
with null next; PATCH daily produces a 03:00 next-fire; PATCH
weekly without weekly_day → 400; PATCH off normalizes lingering
per-mode fields to NULL; non-admin → 403.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
