Guide visibility is now scoped by PORTAL first and role second:
- the buyer portal lists shared and buyer guides, even for an admin, because it
is the buyer portal; admin guides never surface there
- the ops portal lists shared and ops guides, plus admin guides for an
admin/superuser
- the detail view names its context object, so guide pages get a real browser
title instead of a blank one
Link rewriting, so one page can serve both the wiki and the in-app help centre:
- absolute /en/user-guides/... links become the in-app help path
- other absolute /en/... links point at the wiki itself; the app hosts serve no
/en/ routes, so leaving them untouched was a 404 for whoever clicked
- relative links keep their existing behaviour
Tests cover the new rewriting and the portal scoping rules. Also adds
docs/USER_GUIDES_VIEWER_SPEC.md, the spec this viewer was built to.