DIY Smart home project: Restoring the wall switch (opens in new tab)

Background In a previous post, I wrote about building a presence sensor to automatically turn my bedroom lights on and off (smart bulbs connected to Home Assistant). However, I still had to solve the wall switch problem. Problem A normal light switch interrupts mains power to the bulb. This is really bad for smart bulbs. They need continuous power to stay connected to the network (WiFi, in my case), which allows them respond to commands. So every time the wall switch is flipped, it cuts power...