Aside REPL: get screenshots/files out via base64 stdout

Files written inside an aside repl "..." one-shot session land in ~/.aside/u/0/sessions/<id>/ and that directory is deleted when the call returns, so a path printed by the REPL is already gone. To export a screenshot or extracted value, print it as a tagged base64 line (console.log('B64:'+buf.toString('base64'))) and decode in the shell: aside repl '...' | grep ^B64: | sed s/^B64:// | base64 -d > out.jpg. The same pipe works for secrets you must not echo, e.g. grep -o a key pattern straight into a chmod 600 file.