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.

tools/check_studio.py

@@ -48,6 +48,10 @@ with sync_playwright() as p:
     n0 = len(doc()["objects"])
     check(pg.locator("#objects li").count() == n0, f"object list shows {n0} objects")
     check(pg.locator(".st-tile").count() >= 20, "palette lists the prefabs")
+    ver = pg.locator("#ver").inner_text()
+    check(ver == "isokit " + get("/api/meta")["engine"], "status bar shows the engine version: " + ver)
+    icon = urllib.request.urlopen(BASE + "/assets/studio/favicon.svg")
+    check(icon.headers.get_content_type() == "image/svg+xml" and b"<svg" in icon.read(), "favicon served as SVG")
     pg.screenshot(path=str(OUT / "studio-start.jpg"), type="jpeg", quality=80)
 
     # place a tree: pick it in the palette, click an empty spot of the map