Surface report.meta provenance as a compact muted caption above the advisory
disclaimer: «Прогноз рассчитан: <дата> · горизонты N / M мес · схема X». The
freshness date sources from the run's persist time (envelope created_at, always
set) with meta.generated_at as fallback — the deterministic assembler leaves
generated_at null, but created_at is the real compute timestamp. Until now this
provenance lived only in exports; horizons appeared only via the chart axis.
New ForecastMetaLine.tsx: three independently-guarded segments (RU long date
with optional non-midnight time, horizons, most-muted schema); graceful null
when meta empty / 202-pending. Advisory disclaimer stays last.
Part of #958.
