feat(lexicon-resolver): add live lexicon validation
Complete lexicon validation implementation with live DNS-based schema resolution.
Key features:
- DNS authority lookup via _lexicon.{domain} subdomain
- DID resolution to PDS endpoint
- Recursive ref resolution (fetches all referenced schemas)
- Bundled core com.atproto schemas (strongRef, label.defs, moderation.defs)
- Cloudflare Workers compatibility (fetch binding fix)
Changes:
- Add @pds/lexicon-resolver package with DNS/DID resolution
- Add LexiconResolverPort to core PDS
- Validate records in createRecord, putRecord, applyWrites
- Return validationStatus: 'valid' | 'unknown' in responses
- Add default LexiconResolver to node, deno, cloudflare adapters
- Add e2e test for live lexicon resolution
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>