Clicking the wiki magic-link email was producing SessionNotFound:
'interaction session id cookie not found' from
provider.interactionFinished, because that call requires the short-lived
_interaction cookie to be present on the request. It isn't, when:
- the user clicks the email on a different device or browser
- the interaction cookie already expired
- the user is in private/incognito browsing
Those unhandled errors previously bounced to /coming-soon via the
coming-soon middleware, stranding users on the pre-register page.
Instead of relying on the interaction cookie at the magic-link step:
1. Verify the JWT, look up the member, set the auth-token cookie.
2. Redirect the user back to https://wiki.ghostguild.org.
3. Outline re-initiates OIDC, which creates a fresh interaction whose
cookie IS present on the same request, and [uid].get.ts SSOs the user
in via the auth-token cookie we just set.
Also swap the createError throws for sendRedirect to /auth/oidc-error so
token/member/status failures land on the styled error page rather than
Nitro's default unhandled-error response.
Add oidc-provider with MongoDB adapter so ghostguild.org can act as
the identity provider for the self-hosted Outline wiki. Members
authenticate via the existing magic-link flow, with automatic SSO
when an active session exists. Includes interaction routes, well-known
discovery endpoint, and login page.
