Function ResolveInteractivity

Decides whether this run may prompt, most explicit signal first:

1. --no-interactive → never
2. --interactive → yes, if there is a terminal to prompt on
3. INTERACTIVE_ENV → the same, one level down
4. no terminal on stdin or stdout → never
5. a CI environment variable is set → never
6. TERM=dumb → never
7. otherwise → yes; a real terminal means a human

Note the asymmetry at steps 2 and 3: asking for interactivity without a terminal resolves to NON-interactive with reason no-tty rather than throwing. The caller is then free to fail at the exact point a value is missing, which is far more actionable than a blanket "no TTY" error at startup.