feat: destructive reconciliation - #1822

CLA

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• Code changes are tested

Description of the changes, What, Why and How?

Adds destructive reconciliation of the channel message list. On reconnect/rehydrate, messages that were hard-deleted by anyone while the client was offline are removed from the list, for the channel main list and thread replies, with offline support enabled or disabled.

A hard delete emits no event to other clients, and the newest page merge is additive (it never removes), so a message deleted while you were offline lingers as a ghost forever after reconnect and with offline support on, it also survives in SQLite and returns on cold start.

Reconciliation is folded into the existing newest page merge, so every reseed path (channel.query, channel list hydrate, channel.reload, Thread.reload, recoverState) reconciles uniformly, without a full reload and without dropping already-loaded older pages. A loaded message that's absent from the authoritative page is pruned; a prefetch snapshot distinguishes a genuine hard-delete from a message that arrived live during the fetch, and local (optimistic/failed/error) messages are always kept. Reconciled ids are mirrored into the offline DB so a cold start doesn't reseed them. I've also added a billion unit tests that should capture this behaviour because it's an incredible pain to test all of the nooks and crannies here.

Changelog

• Feature: hard deletes performed by other users while you were offline are now removed from the message list (and threads) on reconnect/re-hydrate instead of lingering as ghosts, so no full reload and mirrored into the offline DB so they don't return on cold start.