Stable twin of #1184. Both photo sweeps tracked whether they were running in a
module-level variable, which is invisible to every other replica: a status poll
routed to an idle replica reports isRunning false while another is mid-run, and
the next POST starts a second pass over the whole library.
Migration 179 adds one row per job, claimed with a conditional UPDATE whose
affected-row count is the answer. The lease is fenced on a per-claim token so a
runner superseded by a stale takeover cannot renew a claim it has lost or
release one it no longer owns; renewal runs on a timer spanning the claim
through release, since one hung NAS read can outlast the stale window inside a
single iteration. maintenance_jobs is excluded from .picpeak archives.
Gated on settings.edit / settings.view rather than main's system.manage, which
does not exist on this branch — they are what settings.edit was later split
into, so both branches let the same people through.
Co-authored-by: Paul Nothaft <[email protected]>
