fix(auto-update): CI failures on Linux

- Keep the setup result when chown fails. CI runs as a non-root user, where
  chown to the web user raises; that discarded the result file, so the
  General tab would never learn whether setup worked. Regression test added.
- Register the two new /api/v3/system/auto-update routes in the URL map
  snapshot.
- Use utility classes app.css defines (space-y-1, hover:text-red-600).

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

web_interface/templates/v3/partials/overview.html

@@ -8,7 +8,7 @@
         <p class="text-sm text-red-700 mt-1" id="auto-update-banner-text"></p>
         <p class="text-xs text-red-600 mt-1">Details are under Automatic Updates on the General tab.</p>
     </div>
-    <button type="button" onclick="window.dismissAutoUpdateBanner()" class="ml-4 flex-shrink-0 text-red-500 hover:text-red-700" aria-label="Dismiss">
+    <button type="button" onclick="window.dismissAutoUpdateBanner()" class="ml-4 flex-shrink-0 text-red-500 hover:text-red-600" aria-label="Dismiss">
         <i class="fas fa-times"></i>
     </button>
 </div>