sendRequestMutation and cancelMutation were awaiting query invalidation
in onSuccess, which blocked mutateAsync until 3+ network refetches
completed (~1s+ delay). This caused noticeable lag on send/link/cancel
operations. Now all mutations use sync fire-and-forget invalidation,
matching respondMutation's pattern.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>