Add an accessibility summary page

And link it from the page footer.

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: ctrueden

_includes/layout/footer

@@ -7,6 +7,7 @@
   </ul>
   <ul class="copyright">
     <li>Design: <a href="http://html5up.net">HTML5 UP</a></li>
+    <li><a href="/accessibility">Accessibility</a></li>
   </ul>
 </section>
 

_pages/accessibility.md

@@ -0,0 +1,51 @@
+---
+title: Accessibility
+description: Accessibility conformance statement for the ImageJ wiki.
+---
+
+## Conformance status
+
+This website (imagej.net) targets **WCAG 2.1 Level AA** conformance.
+
+Since March 2026, automated WCAG 2.1 AA checks run on every commit via
+continuous integration, using [pa11y](https://pa11y.org/) with the
+[axe](https://github.com/dequelabs/axe-core) engine. The site currently
+passes all checks that axe can definitively confirm (i.e. excluding issues
+flagged `needsFurtherReview`), except for the `nested-interactive` rule,
+which is ignored for the moment due to the design of the site's main menu.
+
+### Known limitations
+
+- The **home page** has background-image sections where color contrast and
+  link-in-text-block rules are flagged as *needs further review* by axe
+  (meaning axe cannot definitively determine a pass or fail). These sections
+  use image backgrounds with overlaid text; the visual contrast is sufficient
+  in practice but cannot be confirmed automatically.
+- **Nested interactive elements** (e.g. links inside `<summary>` elements
+  generated by third-party themes) are suppressed site-wide, as this pattern
+  is not feasible to fix without upstream changes.
+- Automated tools catch approximately 30–40% of WCAG issues. A full manual
+  audit and screen-reader review have not yet been completed.
+
+## Scope
+
+This statement covers **imagej.net** (the ImageJ wiki). It does not cover:
+
+- **fiji.sc** — the Fiji project website (maintained separately, with its
+  own accessibility improvements)
+- **The Fiji/ImageJ desktop application** — a Java/Swing GUI application
+  whose accessibility depends on the platform's native accessibility APIs
+  and is outside the scope of this website
+
+## Feedback
+
+If you encounter an accessibility barrier on this site, please open an issue
+at [github.com/imagej/imagej.github.io](https://github.com/imagej/imagej.github.io/issues)
+or post on the [Image.sc Forum](https://forum.image.sc/tag/imagej).
+
+## Technical information
+
+This site is a static website built with [Jekyll](https://jekyllrb.com/) and
+hosted on [GitHub Pages](https://pages.github.com/). Accessibility checks use
+[pa11y](https://pa11y.org/) with the [axe-core](https://github.com/dequelabs/axe-core)
+runner against the WCAG2AA standard.