Audit of write-actions revealed that send (and edit via realtime UPDATE) are
already optimistic via local state insertion in `useConversationMessages`,
and friend nicknames are pure-local localStorage. Five user-write actions
were waiting on the ~100-200 ms server roundtrip + realtime echo:
* Toggle mute (`setConversationMutedUntil`)
* Toggle mentions-only (`setConversationMentionsOnly`)
* Toggle archive (`setConversationArchived`)
* Pin / unpin message (`pinMessage` / `unpinMessage`)
* Revoke device (`revokeDevice` RPC)
All five now flip local state synchronously and roll back on failure. The
existing realtime subscriptions reconcile canonically (no-op when the
optimistic patch already matches the server row), so this is purely a UX
latency improvement — no protocol or persistence changes.
Reactions (`toggleReaction` / `voteExclusive`) were intentionally skipped
this round: rollback semantics for the exclusive-vote path with multiple
sequential awaits are messy enough to warrant a dedicated pass.
byGalax