fix(dashboard): pin the Today hero to the skeleton during hydration

The digest query rehydrates from the persisted client cache, so the Today
hero was painting on the first client render while the server had rendered the
skeleton — a text-content hydration mismatch (React #418) that the dashboard
e2e's no-significant-errors gate caught. Gate the hero on `mounted` like the
rest of the dashboard's late-hydrating surfaces, so SSR and the first client
render both show the skeleton and the hero appears once mounted.

src/app/page-client.tsx

@@ -793,7 +793,12 @@ export default function DashboardPageClient() {
           degrades to nothing (the hero itself returns null). The dense
           tile grid + charts below are untouched. */}
       {insightsEnabled &&
-        (digestQuery.isLoading ? (
+        // `!mounted` pins the SSR pass AND the first hydration render to the
+        // skeleton (v1.16.4 pattern): the digest query rehydrates from the
+        // persisted cache on the client, so without this gate the client's
+        // first render would paint the hero while the server rendered the
+        // skeleton — a text-content hydration mismatch (React #418).
+        (!mounted || digestQuery.isLoading ? (
           <TodayHeroSkeleton />
         ) : digestQuery.data ? (
           <TodayHero digest={digestQuery.data} />