feat: batch Instagram import writes with applyWrites
Switch import from individual createRecord calls to batched applyWrites,
reducing round trips from N+1 to 2 per post. Bump hatk to alpha.57 which
includes the applyWrites proxy and a fix for firehose commit indexing
that matched blocks by $type instead of by CID.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>