Adds a "Scan schedule" section to the admin overview page between
the existing Library Scan and Cover Art sections. Mode picker
(Off / Every N hours / Daily / Weekly) with conditional interval /
time / day inputs. Save button disabled until local state diverges
from the server state. "Next scan: in N hours (timestamp)"
inline indicator when mode != off.
formatRelative is a static helper (recomputes on render); operator
sees the configuration confirmation at a glance — not a countdown
timer.
admin.test.ts mock extended with createScanScheduleQuery returning
mode='off' default. New test asserts the section renders. Existing
assertions still pass.
bvandeusen
6a2697518f