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_web.py

@@ -89,6 +89,11 @@ try:
         check(pg.evaluate("() => getComputedStyle(document.querySelector('.iso-svg .iso-t')).fill") not in ("", "rgb(0, 0, 0)"),
               "theme CSS styles the scene")
         check(pg.evaluate("() => isokit.webmcp") == 15, "15 MCP tools registered with WebMCP")
+        ver = pg.locator("#ver").inner_text()
+        check(ver.startswith("isokit " + pg.evaluate("() => isokit.engine") + " · "), "status bar shows version and build: " + ver)
+        icon = pg.evaluate("""async () => { const l = document.querySelector('link[rel=icon]');
+            const r = await fetch(l.href); return r.ok && (await r.text()).includes('<svg'); }""")
+        check(icon, "favicon link loads an SVG")
         shot(pg, "web-start.jpg")
 
         # ---------------------------------------------------------------- edit: place, drag, props, undo