Bump version to v2026.9.8.3

Same-day patch release: adds the in-app User Guide and standalone
User Guide PDF.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

packaging/linux/org.darksingularity.OrbitHub.metainfo.xml

@@ -34,6 +34,12 @@
     </screenshot>
   </screenshots>
   <releases>
+    <release version="2026.9.8.3" date="2026-09-08">
+      <url>https://git.darksingularity.org/DarkSingularity/orbithub/releases/tag/v2026.9.8.3</url>
+      <description>
+        <p>Adds an in-app User Guide (Help -> User Guide) and a standalone User Guide PDF.</p>
+      </description>
+    </release>
     <release version="2026.9.8.2" date="2026-09-08">
       <url>https://git.darksingularity.org/DarkSingularity/orbithub/releases/tag/v2026.9.8.2</url>
       <description>