Accelerate Reference Spine Overview Lists

The owner console overview and runs pages block on reference spine list routes. Live measurement after the connector-summary fix showed /ref/traces at about 365-900ms and /ref/runs?limit=100 at about 700-950ms. The traces route was doing a full aggregate over roughly 579k spine events to show six recent rows.

The dashboard home needs a small "what has been read" list and the runs page needs a recent run list. Those are overview reads. Before this change, Postgres computed them by grouping every matching spine_events row, sorting the full aggregate, then hydrating each summary sequentially.

The reference implementation SHALL serve unfiltered first-page reference spine correlation lists (/ref/traces, /ref/runs, and /_ref/grants) from a bounded recent-correlation read path on Postgres. Filtered and cursor-paginated reads SHALL preserve the existing aggregate semantics.