Tablet kitchen reading mode (2a) (Feature 15) (#149)

Co-authored-by: orchestrator-agent <20+orchestrator-agent@code.cubecraftcreations.com>

web/src/dinners/keepScreenOn.ts

@@ -0,0 +1,10 @@
+import { useState } from 'react'
+
+// useKeepScreenOn is Kitchen reading mode's Keep screen on switch: whether it
+// is on, and a setter. It starts off on each visit.
+//
+// TODO(c7da10dc): hold a Screen Wake Lock while it is on. Today it is only
+// the switch's state; nothing keeps the screen awake yet.
+export function useKeepScreenOn(): [boolean, (on: boolean) => void] {
+  return useState(false)
+}