* Run the channel message backfill in the background after startup
* Finish each backfilled packet; mark packets whose message exists; log a shutdown stop
* Cap each backfilled packet's statements at 30 s
* feat(db): channel_message_iatas table and indexes
* feat(ingest): record channel message sites at insert and on every later hearing
* feat(db): channel message site backfill and two-range reconcile
* feat(db): serve region and scope message pages from the site read model when trusted
* feat: boot repair, periodic reconcile and first-time verification for the message site read model
* test(planguard): channel message site statements, diff and storediff cases
* feat(background): log when a read-only server trusts the message site read model
* test(planguard): storediff vars in query values, and message cases read from the data
* fix(ingest): record a stored hearing's channel message site right after the observation insert
* fix: bounded message dispatch for filtered all-channel pages, fresher read-only trust, earlier invalidation
* fix: record a hearing's site after its path is marked and skip the backstop when the message was found; read-only trust ends at the writer's deadline
MrAlders0n