fix(site): track the install copy button with data-umami-event

Every other homepage link is tracked declaratively; the copy button
called window.umami directly, and only on success, so failed copies never
showed up in the stats.

website/.vitepress/components/HomePage.vue

@@ -43,19 +43,11 @@ async function copyInstallCommand() {
   try {
     await navigator.clipboard.writeText(installCommand);
     copyState.value = 'copied';
-    track('home-install-copy');
   } catch {
     copyState.value = 'failed';
   }
   resetCopyState();
 }
-
-function track(event: string) {
-  const analytics = (
-    window as Window & { umami?: { track: (name: string) => void } }
-  ).umami;
-  analytics?.track(event);
-}
 </script>
 
 <template>
@@ -76,6 +68,7 @@ function track(event: string) {
         <button
           type="button"
           :aria-label="copyAriaLabel"
+          data-umami-event="home-install-copy"
           @click="copyInstallCommand"
         >
           {{ copyLabel }}