fix(setup): skip auto-launch without interactive stdin

[sgaofen]

Summary

• guard the post-setup hermes chat handoff behind an interactive-stdin check
• keep the existing execvp fast path for interactive terminals
• add regression coverage for the new non-interactive fallback and preserve the existing interactive launch test

Fixes #8641.

Testing

• python3 -m py_compile /Users/stephenyu/Documents/hermes-agent-wt-8641/hermes_cli/setup.py /Users/stephenyu/Documents/hermes-agent-wt-8641/tests/hermes_cli/test_setup.py
• uv run --directory /Users/stephenyu/Documents/hermes-agent-wt-8641 --extra dev pytest -o addopts= /Users/stephenyu/Documents/hermes-agent-wt-8641/tests/hermes_cli/test_setup.py -k 'offer_launch_chat'

Platform Tested

• macOS 15.x (Apple Silicon)

Contribution Guide Notes

• Reviewed CONTRIBUTING.md and checked for existing open PRs before submitting this scoped change.
• Ran the targeted verification commands listed above for this PR. I have not claimed a full repo-wide pytest tests/ -q pass unless explicitly noted.

[alt-glitch]

Likely duplicate of #8420 — both guard post-setup chat launch in non-interactive stdin environments.

[teknium1]

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

Triage notes (high confidence):
Commit 256bedb (#25067 'fix(setup): drop post-setup chat handoff') removed _offer_launch_chat entirely from hermes_cli/setup.py; the function the PR patches no longer exists on main.

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.)