Add Spine Events Source Run Summary Index

listSpineCorrelations aggregates spine_events by correlation id and supports source filters. Postgres already carries a source/run summary index for that hot path; SQLite lacked equivalent coverage.

The aggregation hot path builds a GROUP BY query over spineevents, applying stable filters such as sourcekind and sourceid before hydrating bounded summary rows. Postgres bootstrap and migration DDL already include idxpgspineeventssourcerun_summary for the source-filtered run summary shape.

The reference implementation SHALL provision equivalent SQLite and Postgres spine_events index coverage for source-filtered run-summary aggregation.