altunsumerve/sstv-lab ? reverse-engineered prompt

Build me a simple browser app that lets people try SSTV with no special equipment. I want one screen for sending a photo as sound using the built in speaker, and one screen for listening with the microphone and rebuilding the image line by line. It should use Robot36 only, work with a phone and a computer, and feel easy enough for someone with no radio background to try right away.

Please keep everything running in the browser so photos and microphone audio stay on the device. Include a test card so I can try it without choosing a photo, and let me save the received image as PNG. Make it clear how to start listening, how to play the audio, and remind people to keep the devices close together and the volume reasonable. If you need current browser or audio API details, look them up online.