fix: Soften force shutdown message (#13104)
### Why
The forced shutdown message is part of normal Ctrl+C handling and should
not look like a loud warning in the terminal.
### What
Render the force-shutdown status using the same dim Turborepo status
styling as the graceful shutdown prompt, and update the wording to say
tasks were force killed.
### How
Verified with `cargo test -p turbo --test graceful_shutdown_test
run_force_kills_on_second_sigint_in_tty`.
