rename topnav to navbar

This one of the parts of the change to the [look and feel
change](https://github.com/ioccc-src/temp-test-ioccc/issues/2273#issuecomment-2059754857)
wrote about.

Stay tuned ...

inc/navbar.year.first.html

@@ -0,0 +1,10 @@
+<!-- START: this line starts content from: inc/navbar.year.first.html -->
+
+<div class="navbar">
+  <a class="Left Disabled" href="#">No prev</a>
+  <a class="Left" href="%%UP_LINK%%">&uarr; %%UP_TEXT%% &uarr;</a>
+  <a class="Left" href="%%RIGHT_LINK%%">%%RIGHT_TEXT%% &rarr;</a>
+  <a class="Right" href="%%INVENTORY_LINK%%">%%INVENTORY_TEXT%%</a>
+</div>
+
+<!-- END: this line ends content from: inc/navbar.year.first.html -->