Get Schedules Pending Summary

ONE call for the publish state of every track on the event.

Per schedule: the draft-vs-latest-published-snapshot diff (same lenient normalizers as the frontend's useSchedulePendingCounts — ports of their hash functions, applied server-side where both serializations come from the same code path, so they never drift), the pending proposal changes (enriched, ready for the Actions feed), and a minimal activity projection (id/title/speaker/sponsor ids) for session identity rows.

Replaces the frontend's 2N per-track GET fan-out (versions + activities per schedule) purely to light up publish dots.