Overlays live pending_started_at/updated_at/last_message_at onto cached /api/sessions rows
(when newer), sorts active/running sessions first then by freshest effective timestamp, applies
the same running-first order in the frontend sidebar renderer, and groups date buckets with the
same runtime-aware timestamp (no stale header on resumed running sessions). routes.py +
sessions.js + 81-line test. Composes with #4680 cache-freeze + #4597 (98 session-list tests pass).
Co-authored-by: nesquena-hermes <agent@nesquena-hermes>
Co-authored-by: franksong2702 <franksong2702@users.noreply.github.com>
