Add 7 missing subpath exports to @gsd/native (diff, gsd-parser,
highlight, json-parse, stream-process, truncate, ttsr) and create
root-level oauth.js/oauth.d.ts stub files for @gsd/pi-ai to match
the bedrock-provider pattern.
Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
