Widgets tab links the external demo when config.json names one (demo_url)

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

web/src/Gallery.tsx

@@ -31,7 +31,7 @@ function Tile({ spec, data, note }: { spec: WidgetSpec; data: WidgetData; note:
   )
 }
 
-export default function Gallery() {
+export default function Gallery({ demoUrl }: { demoUrl?: string }) {
   const [cat, setCat] = useState<Sensor[] | null>(null)
   const [err, setErr] = useState('')
   const rate = useRefreshMs()
@@ -54,7 +54,11 @@ export default function Gallery() {
 
   return (
     <div className="dash gallery">
-      <div className="dash-bar"><span className="hint">{sensors.length} sensors on this machine · live · tap a tile to copy its ID</span></div>
+      <div className="dash-bar">
+        <span className="hint">{sensors.length} sensors on this machine · live · tap a tile to copy its ID</span>
+        <span className="spacer" />
+        {demoUrl && <a className="btn" href={demoUrl} target="_blank" rel="noreferrer" title="a page outside Ham Lab, built on the same sensor API">External demo ↗</a>}
+      </div>
 
       <h2 className="section">Widget types</h2>
       <div className="kpis">