Verify the ledger

Replays signatures, body hashes and hash-chain continuity for the workspace the calling key belongs to.

valid has three values, not two. true verified and false broken are findings about the chain; null means no verdict was produced, because there was no key to check authorship against. reason says which case it is. A key that is stored but cannot be read is a configuration problem, reported in warnings, not a finding about the chain.