fix: restore terminal state on Ctrl+C during interactive task selection

[kazupon]

resolve #305

• Replace std::process::exit(130) with a SelectResult::Cancelled return value so that RawModeGuard::drop() runs and disable_raw_mode() is called properly
• Previously, pressing Ctrl+C during interactive task selection (vt run without a task specifier) left the terminal in raw mode (-opost), causing staircase rendering for all subsequent commands
• Add CtrlC variant to the e2e WriteKey enum and an "interactive ctrl-c cancels" test to verify exit code 130

[branchseer]

Thank you!