When running `hermes gateway install` on Linux/systemd, the command
unconditionally prompts with two `prompt_yes_no` questions, breaking
headless installs (SSH, CI, provisioning scripts) and ignoring the
existing --start-now / --start-on-login CLI flags that the Windows
branch already respects.
The fix mirrors the Windows path: read CLI flags first, prompt only
when flags are not provided AND stdin is a TTY, and fall back to True
defaults for non-TTY contexts. The argparse help strings are promoted
from SUPPRESS to visible so users can discover the flags.
Fixes#42065
831d443b03