feat(streamer): react views ported from prototype with sse hooks

streamer/src/views/shared/useElapsed.ts

@@ -0,0 +1,10 @@
+import { useEffect, useState } from "react";
+
+export function useElapsed(startedAt: number, duration: number): number {
+  const [now, setNow] = useState(() => Date.now() / 1000);
+  useEffect(() => {
+    const t = setInterval(() => setNow(Date.now() / 1000), 200);
+    return () => clearInterval(t);
+  }, []);
+  return Math.min(duration, Math.max(0, now - startedAt));
+}