v0.2.0 - Full text query output and stdin index support

New features:
- Query results now include full document text alongside metadata,
  removing the need for a separate lookup step after search
- Index command accepts document paths from stdin, enabling
  piped workflows (e.g. find ... | gapvec index -)

These changes support the Den's context assembly pipeline where
dkg feeds document paths to gapvec for incremental indexing, and
query consumers need complete text without round-tripping back
to the filesystem.