lib/upload.ts provides uploadScreenshot() that uploads to Supabase
Storage and returns a public CDN URL. Falls back gracefully to local
path with stderr warning on any failure (no config, expired auth,
network error). Exit code 0 always — never breaks calling templates.
bin/gstack-upload is a thin bash wrapper for CLI use.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Garry Tan