test: add initial test files and component stubs

src/containers/DigitalClock.tsx

@@ -0,0 +1,13 @@
+import { useState } from 'react';
+import { useCurrentTime } from '../hooks/useCurrentTime';
+import { dateToDigital } from '../utils';
+
+interface DigitalClockProps {
+  enabled: boolean;
+}
+
+export function DigitalClock({ enabled }: DigitalClockProps) {
+  const { currentTime } = useCurrentTime();
+  const digital = dateToDigital(currentTime);
+  return null;
+}