Only rp-id and rp-name are essential bootstrap-time configuration;
origins and auth hosts are set up afterwards via the admin interface.
Removes --origin/--auth-host from init and from devserver, and the
now-unused hostutil.validate_auth_host.
RealmConfig.origins is again purely an allow-list of sign-in sites
within the realm's domain (unset = rp-id and all subdomains), restoring
the restriction semantics the realm rework had silently turned into an
always-open subtree. Cross-domain ROR origins move to their own
RealmConfig.related_origins field — always additive, capped, validated
to be outside the rp-id domain, and the sole source of the
/.well-known/webauthn document.
Admin API POST/PATCH accept related_origins; misfiled entries are
rejected (cross-domain in origins, in-domain in related_origins).
Admin UI: the realm dialog edits the two lists separately with
end-user-oriented explanations (allowed sign-in sites vs. related
domains + the well-known note); the Realms section intro explains the
multi-domain model, and the table shows sign-in site and related domain
counts.
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