fix: standard.site is a lexicon, not a platform
- remove standardsite from PLATFORM_CONFIG
- only show platform badge for actual platforms (leaflet, pckt, offprint)
- add universal fallback URL via pdsls.dev for all documents
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>