Serve never converts databases: with no paskia.kantadb it points at
'paskia init', or at 'paskia migrate' when legacy *.paskiadb candidates
exist. migrate converts a lone candidate, or the one named by --rp-id
when several exist; the rest stay in place. devserver fails fast with
the same hint. gitignore covers paskia.kantadb and *.converted-bak.
README quick start and configuration updated for init/serve split and
paskia.kantadb; API.md server-config endpoints replaced with admin realm
CRUD and the well-known webauthn endpoint; proxy guides point at the
realm auth-host setting; oidc.md documents per-realm issuers; MultiSite.md
rewritten from the implementation plan into documentation of the shipped
mechanics, policy model, and design rationale.
LeoVasanko