fix(setup): reattach tty before launching chat

[LeonSGP43]

Summary

• reattach setup stdin to a real terminal before auto-launching hermes chat
• fall back to the existing manual instruction when no terminal can be reopened
• add regression tests for the tty reattach path and the fallback path

Testing

• pytest -o addopts='' tests/hermes_cli/test_setup.py -k 'offer_launch_chat or reattach_stdin_to_tty'

Closes #12074

[teknium1]

Closing as stale — the code path this addresses no longer exists on main.

Triage notes (high confidence):
Merged PR #25067 'fix(setup): drop post-setup chat handoff' removed the auto-launch hermes chat code path entirely; the _reattach_stdin_to_tty/_offer_launch_chat functions this PR adds no longer have a caller in main hermes_cli/setup.py.

If this PR's intent is still relevant against the current code, please rebase or open a fresh PR.

(Bulk-closed during a CLI PR triage sweep.)