Portal v0.6.24; lint with portal itself

The instance ran v0.5.2 while the portal is at v0.6.24, which is where
`slideshow` and the sign-in row on the wordmark's line came in. The
lint is now the portal binary at the pinned release, as Klingenberg
Bygg's is, so what passes CI is what the running instance accepts
(site.yaml included; iris stopped at v0.5.10).

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

README.md

@@ -14,4 +14,5 @@ it existed. Norwegian is the source language.
   `naerbilde.jpg` (Jannicke) is missing because it 404s on the source
   site itself — ask for a replacement.
 
-Lint before pushing: `question_lint --path questions`.
+Lint before pushing: `portal lint --path questions`, with the portal
+release `.gitea/workflows/deploy.yml` pins.