Improve pagination nav with disabled state and accesskeys (#469)

Author: julioest

antora-ui/src/css/pagination.css

@@ -86,3 +86,9 @@ Spirit style navigation
   border-width: 0;
   vertical-align: middle;
 }
+
+.spirit-nav .disabled {
+  opacity: 0.35;
+  cursor: not-allowed;
+  pointer-events: none;
+}

antora-ui/src/partials/pagination-spirit.hbs

@@ -1,11 +1,21 @@
 <div class="spirit-nav">
   {{#with page.previous}}
-    <a accesskey="p" href="{{{relativize ./url}}}"><span class="material-symbols-outlined" title="Previous: {{{./content}}}">arrow_back</span></a>
-  {{/with}}
-  {{#with page.parent}}
-    <a accesskey="p" href="{{{relativize ./url}}}"><span class="material-symbols-outlined" title="Up: {{{./content}}}">arrow_upward</span></a>
+    <a accesskey="p" href="{{{relativize ./url}}}">
+      <span class="material-symbols-outlined" title="Previous: {{{./content}}}">arrow_back</span>
+    </a>
   {{/with}}
+  {{#if page.parent}}
+    <a accesskey="u" href="{{{relativize page.parent.url}}}">
+      <span class="material-symbols-outlined" title="Up: {{{page.parent.content}}}">arrow_upward</span>
+    </a>
+  {{else}}
+    <a class="disabled" accesskey="u" aria-disabled="true" tabindex="-1">
+      <span class="material-symbols-outlined" title="Up:">arrow_upward</span>
+    </a>
+  {{/if}}
   {{#with page.next}}
-    <a accesskey="p" href="{{{relativize ./url}}}"><span class="material-symbols-outlined" title="Next: {{{./content}}}">arrow_forward</span></a>
+    <a accesskey="n" href="{{{relativize ./url}}}">
+      <span class="material-symbols-outlined" title="Next: {{{./content}}}">arrow_forward</span>
+    </a>
   {{/with}}
-</div>
+</div>