Make scene selection in Encode automatic

[andreamorales]

Description
I believe we should make the selection of scenes in Encode automatic so people don't get confused about the fact that they don't have any agency over the process of encoding a seed in scenes. It should look like this (from my Figma file)

Please note the text in Encode should be "We are automatically encoding your key inside SeedQuest's worlds."

[andreamorales]

I also want to indicate that this means the numbers on the buttons should be eliminated altogether in both Encode and Decode scene select. Thank you!