Refreshes the vendored lexicon JSON files under priv/lexicons from
their upstream sources and records the pinned revisions in
priv/lexicons/SOURCES.md.
Sources:
app/bsky/**andcom/atproto/**: the full corpora from github.com/bluesky-social/atproto at the latestmaincommit (the resolved commit is recorded). Every upstream lexicon file is vendored, so new schemas appear on the next sync.community/**: full corpus. The file list comes from the GitHub mirror (lexicon-community/lexicon); every file downloads from Tangled, the canonical source. New community lexicons appear on the next sync.
After syncing, run mix exosphere.gen.lexicons to regenerate modules and
review the diff.