Versioned ShardAdapter ABC (shard_id/profile/keys/read mandatory; optional verbs
raise NotSupported by default = honest absence). FolderAdapter reads a dir of
Markdown into Pages (relpath=key, mtime=source_rev, provenance envelope),
declaring a validated read-only file-store profile. 4 tests green.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
