docs: link to GitHub release notes and add releases page

- Update announcement banner to link to GitHub release instead of local page
- Add /reference/releases page listing all lexicon releases
- Add Releases entry to sidebar navigation
- Remove local release notes page (release-notes-v0-11-0.md)

Author: s-adamantine

components/AnnouncementBanner.js

@@ -24,9 +24,9 @@ export function AnnouncementBanner() {
         <span className="announcement-banner-date">April 8, 2026</span>
         <span className="announcement-banner-text">
           <strong>hypercerts-lexicon v0.11.0</strong> — breaking changes to evaluation scores, badge references, and funding receipts.{' '}
-          <Link href="/reference/release-notes-v0-11-0" className="announcement-banner-link">
+          <a href="https://github.com/hypercerts-org/hypercerts-lexicon/releases/tag/v0.11.0" className="announcement-banner-link" target="_blank" rel="noopener noreferrer">
             Read the release notes&nbsp;&rarr;
-          </Link>
+          </a>
         </span>
         <button
           className="announcement-banner-close"

lib/navigation.js

@@ -161,10 +161,7 @@ export const navigation = [
           },
         ],
       },
-      {
-        title: "Lexicon v0.11.0 Release Notes",
-        path: "/reference/release-notes-v0-11-0",
-      },
+      { title: "Releases", path: "/reference/releases" },
       { title: "Certified PDSs", path: "/reference/certified-pdss" },
       { title: "Certified Services", path: "/reference/certified-services" },
       { title: "Glossary", path: "/reference/glossary" },