Suggest no-args form when has no session to append to

[ncoop57]

When claudedojo -r is run from a directory with no existing Claude transcripts (e.g. a fresh clone), resolve_session raises an unhelpful FileNotFoundError: No session named or identified by None in ..

This wraps the -r path in a try/except FileNotFoundError so the user sees:

No session named or identified by ... in . No session to append to; to prepare a fresh one instead: claude -r $(claudedojo)

sys.exit(str) sends both lines to stderr with exit code 1, so $(claudedojo -r) in command substitution captures nothing rather than a bogus id. Scoped to -r only; --compact still raises bare.