docs site: rewrite directory-style links to their landing pages

A MkDocs hook turns links like [incidents/](incidents/) — which Gitea
renders as a directory listing but a static site would resolve against the
page URL — into links to the generated landing page for that directory.

publishing/build.sh

@@ -34,6 +34,7 @@ tar cf - \
   --exclude='.site-build' \
   --exclude='.venv-docs' \
   --exclude='*.sh' \
+  --exclude='*.py' \
   --exclude='publishing/webhook-receiver.py' \
   --exclude='publishing/webhook-receiver.service' \
   --exclude='mkdocs.yml' \