Campaign.summary was a bare Optional[dict] while RunSummary is a typed VO —
scheduler state (spawned_indices/errors) flowed untyped through
set_/get_summary. Introduce CampaignSummary + SchedulerState (extra=allow,
validate_assignment), mirroring RunSummary; campaign_runner reads/writes the
VO. Also converge the ~10 repeated JSON column get/set pairs onto
_json_dumps/_json_loads helpers, unifying ensure_ascii=False and fixing the
set_modalities ensure_ascii=True trap.
