The contributor's PR silently swallowed ValueError from
SessionDB.set_session_title() with bare except Exception: pass.
Users typing /new <title> with an already-in-use title got an
untitled session and no feedback.
Changes:
- cli.py: catch ValueError from both sanitize_title() and
set_session_title(); print the error and mark the session
untitled in the banner (never echo the rejected title back).
- gateway/run.py: append a warning note to the reset reply on
title rejection; reflect the accepted title in the header.
- Add regression tests for the duplicate-title path in CLI and
gateway.
Also map exx@example.com -> @exxmen in scripts/release.py.
