* feat(db): background_state table and the (hop_count, iata) route index
* perf(db): one /routes statement per filter shape, hop pair on custom plans
* feat(db): keyset route retention and grace slices at exact cutoffs
* feat(background): hourly route retention with a bounded grace walk and watermark
* fix(background): bound the grace walk at microsecond cutoffs
* feat(db): stamp-free reconfirm sweep over the route primary key
* feat(background): pace route reconfirm at routes.reconfirm_rows_per_hour, no stamps
* test(routes): drive route retention end to end and tidy comments
* fix(profiling): sample during the hourly route retention run
Stats endpoints read hourly rollup tables filled once per closed hour by one
advisory-locked task, instead of materialized views that re-scanned every
observation on each refresh. IATA-set tables give exact distinct counts for any
IATA set or region. Cleanup holds raw rows for unrolled hours (up to 24h).
Adds /stats/series; ingest keeps packet observation counts, observer last IATA,
channel message counts and trace tag summaries. 001_baseline.sql is rewritten,
so pre-release 2.0 databases must be recreated. See docs/historical-stats.md.
MrAlders0n