fix(cli,gateway): surface title errors from /new <name>

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.

scripts/release.py

@@ -513,6 +513,7 @@ AUTHOR_MAP = {
     "nftpoetrist@gmail.com": "nftpoetrist",  # PR #18982
     "millerc79@users.noreply.github.com": "millerc79",  # PR #19033
     "hermes@example.com": "shellybotmoyer",  # PR #18915 (bot-committed)
+    "exx@example.com": "exxmen",  # PR #19555
     "hypnosis.mda@gmail.com": "Hypn0sis",
     "ywt000818@gmail.com": "OwenYWT",
     "dhandhalyabhavik@gmail.com": "v1k22",