v0.1.0

Added

• The freighter loader: reads a sharded BigQuery table through the Storage
  Read API and writes one gzipped JSON cell per row to Bigtable in ascending
  key order, with one verdict per shard.
• Manifest format version 3, including row deletes for NULL json
  (null_json_deletes_row).
• Documentation: concepts, preparing a source table, manifest and verdict
  reference, sizing, verifying a load, design notes.
• Release binaries for Linux (x86_64, aarch64, static musl) and macOS, and a
  container image at ghcr.io/faradayio/freighter.