Bump fly VM to shared-cpu-2x / 4 GB
Previous shared-cpu-1x:1024MB was OOM-killed (exit 137) under the
duckdb + sqlite + firehose ingest workload. Switch to the unambiguous
size/memory shortcut so future fly deploys can't accidentally downgrade.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>