External links in post bodies now open in a new tab and show a
box-with-arrow marker icon, so readers can tell at a glance which
links leave the site.
- blogex: new Blogex.ExternalLinks.rewrite/1 marks up anchors with
http(s) hrefs at compile time with target="_blank", rel="noopener"
and class="blogex-external" (idempotent, merges into existing
class/rel values, leaves relative, mailto: and #anchor links alone)
- blogex: Post.build/3 applies the rewrite, so every blog gets it
- app: CSS in .blogex-post-body draws the marker via a mask so it
inherits the link colour; empty ::after content stays invisible
to screen readers
- make test now also runs the blogex suite; it is currently red
with 3 pre-existing blog_integration_test failures caused by the
vacuous link validator (parked yak
link-validator-never-sees-compiled-html-...)