On Linux on Mac there's a command-line program called base64. On Windows, certutil can do it. But if you're command-line-averse there are websites that do it too, e.g. https://www.base64encode.org/
If you don't like base64, you could instead load the textarea with the output of the sqlite3 .dump command, which generates the sql commands to reconstruct the database. That's a text file, so no encoding is required. But you'd have to change the wrapper to start with an empty database and run the SQL commands first, before running the user's SQL.
If you don't like base64, you could instead load the textarea with the output of the sqlite3 .dump command, which generates the sql commands to reconstruct the database. That's a text file, so no encoding is required. But you'd have to change the wrapper to start with an empty database and run the SQL commands first, before running the user's SQL.