studio: version text in the status bar, favicon

The status bar ends with "isokit <engine version>"; the web build adds
the commit (linked on Gitea), its date as a tooltip and a "+" when built
from a tree with uncommitted changes (build_web.py writes a
<meta name="isokit-build"> from GITHUB_SHA or git). /api/meta now carries
"engine". studio/favicon.svg (isometric cube in the accent green) is
served by `isokit studio` (also on /view) and copied into the web build.
check_web.py and check_studio.py check both.

studio/index.html

@@ -9,6 +9,7 @@
 if(t!=="light"&&t!=="dark")t=window.matchMedia&&matchMedia("(prefers-color-scheme: light)").matches?"light":"dark";
 document.documentElement.setAttribute("data-theme",t);})();
 </script>
+<link rel="icon" type="image/svg+xml" href="/assets/studio/favicon.svg">
 <link rel="stylesheet" href="/assets/viewer/isokit-view.css">
 <link rel="stylesheet" href="/assets/theme.css">
 <link rel="stylesheet" href="/assets/studio/studio.css">
@@ -51,6 +52,7 @@ document.documentElement.setAttribute("data-theme",t);})();
       <span class="st-grow"></span>
       <button type="button" id="warnbtn" class="st-link" hidden></button>
       <span id="stats"></span>
+      <a id="ver" class="st-ver" href="https://git.b4l.co.th/B4L/isokit" target="_blank" rel="noopener"></a>
     </footer>
   </section>
   <aside class="st-right" id="right"></aside>