Move highstate_interval_hours to salt.schedule and split schedule.sls

highstate_interval_hours describes the per-minion highstate schedule, not the
active-push pipeline, so relocate it from salt.auto_apply to a new salt.schedule
settings subtree. Repoint so-salt-minion-check at the new pillar path (it had
been left on the stale global:push path) so its restart grace period tracks the
schedule again.

- Add salt.schedule.highstate_interval_hours to defaults.yaml/soc_salt.yaml and a
  side-effect-free salt/salt/schedule.map.jinja (SCHEDULEMERGED), matching the
  *MERGED map convention. Consumers read SCHEDULEMERGED.highstate_interval_hours.
- Split salt/schedule.sls into salt/salt/highstate_schedule.sls (every minion) and
  salt/salt/push_drain_schedule.sls (managers); update top.sls to apply the
  highstate schedule via '*' and the drainer schedule via the configured-manager
  block. Remove the now-empty schedule.sls aggregator.
- pillar_push_map.yaml and so-push-drainer: comment/doc updates only.

salt/reactor/pillar_push_map.yaml

@@ -186,12 +186,12 @@ registry:
     tgt: 'G@role:so-eval or G@role:so-import or G@role:so-manager or G@role:so-managerhype or G@role:so-managersearch or G@role:so-standalone'
 
 # salt: fanout to a fleetwide highstate. The salt.auto_apply settings tune the
-# push pipeline itself (enabled, debounce/drain intervals, batch sizing) and the
-# per-minion highstate schedule; they are consumed by the manager's schedule,
-# beacons, and master reactor config as well as every minion's highstate
-# schedule, so a targeted re-apply isn't meaningful. A salt audit row only fires
-# for SOC-driven salt.auto_apply edits -- salt version bumps go through soup, not
-# SOC, so they never reach this map.
+# push pipeline itself (enabled, debounce/drain intervals, batch sizing) and
+# salt.schedule sets the per-minion highstate interval; they are consumed by the
+# manager's schedule, beacons, and master reactor config as well as every
+# minion's highstate schedule, so a targeted re-apply isn't meaningful. A salt
+# audit row only fires for SOC-driven salt.auto_apply / salt.schedule edits --
+# salt version bumps go through soup, not SOC, so they never reach this map.
 salt:
   - highstate: True
     tgt: '*'