onboarding sandbox: seed real logins/transcripts for import testing

Add 'seed-real-logins' and 'fresh-real' commands to copy your real external
credential files (Codex/Claude/Gemini/Copilot/Cursor/OpenCode/pi) and optional
Codex/Claude transcripts into $JCODE_HOME/external so the onboarding import and
'continue where you left off' steps act on real data. Copies only; originals
untouched. Also ignore /.tmp/ since it can now hold real tokens.