refactor: extract core atproto lexicons to JSON files, add clean build step
Move com.atproto.repo.strongRef, com.atproto.label.defs, and
com.atproto.moderation.defs from inline objects in lexicon-resolve.ts
to src/lexicons/ JSON files. The resolver now loads all built-in
schemas from disk. createReport lexicon references
com.atproto.repo.strongRef instead of a local #strongRef def.
Build now cleans dist/ before compiling to prevent stale artifacts.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>