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/studio.js

@@ -356,12 +356,28 @@
   if (B && B.preview) $("preview").addEventListener("click", function (e) { e.preventDefault(); B.preview(); });
   if (B && B.saveTitle) $("save").title = B.saveTitle;
 
+  // engine version from /api/meta; a web build adds its commit and date
+  // (<meta name="isokit-build" content="<sha> <date> [dirty]">, tools/build_web.py)
+  function showVersion() {
+    var el = $("ver"), m = document.querySelector('meta[name="isokit-build"]');
+    var b = m ? m.getAttribute("content").split(" ") : [];
+    var text = "isokit " + (S.meta.engine || "?"), tip = "isokit engine " + (S.meta.engine || "?");
+    if (b[0]) {
+      text += " · " + b[0].slice(0, 7) + (b[2] ? "+" : "");
+      tip += ", build " + b[0] + (b[1] ? " (" + b[1] + ")" : "") + (b[2] ? ", with uncommitted changes" : "");
+      el.href = "https://git.b4l.co.th/B4L/isokit/commit/" + b[0];
+    }
+    el.textContent = text;
+    el.title = tip;
+  }
+
   // ------------------------------------------------------------ start
   Promise.all([api("/api/meta"), api("/api/doc")]).then(function (rs) {
     S.meta = rs[0]; takeState(rs[1]);
     document.title = S.meta.title + " · isokit Studio";
     $("title").textContent = S.meta.title;
     if (S.meta.load_error) toast(S.meta.load_error, true);
+    showVersion();
     renderPalette(); renderLists(); mountView(); renderRight();
     poll();
   });