.env to JSON / JSON to .env

Single quotes are literal, while double quotes turn \n and \t into real newlines and tabs. Unquoted values only treat a hash preceded by whitespace as a comment, so a#b stays part of the value.

A repeated key keeps the last occurrence, matching dotenv behaviour; the page lists the duplicates.

Nesting splits on a double underscore by default, so DB__HOST becomes two levels. For keys like AWS_SECRET_ACCESS_KEY that use single underscores, leave the separator empty.