Adds cron-like recurring runs (the engine the maintenance-automation work
needs). New AnsibleSchedule model + migration 0018; a core ScheduledTask
(ansible_scheduled_runs, 60s) fires due schedules, each creating a
system-triggered AnsibleRun (triggered_by=None). Centralises the
resolve-inventory → create-run → launch flow in ansible/runner.trigger_run,
shared by the manual route (refactored to use it) and the scheduler.
Schedules UI under /ansible/schedules: create/edit/pause/delete/run-now,
with interval presets, scope targeting (all / group / target), extra-vars /
limit / tags / dry-run, and last-run status (resolved via last_run_id) +
next-run. Unit test for the due-check.
Task #549 (milestone #37).
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
