new: drive the wizard and verification offers through the Prompter port

The interactive half of pkh new no longer touches the terminal prompt
module directly: run() takes a Prompter, picks the wizard or the plain
resolve path through interactive(), and every select/text/confirm
question (including the verification offers) goes through the port.
Cancellations propagate as Err, preserving Ctrl+C-aborts; the summary
and vendoring-notice prints become log lines. A builder-server embed
can now drive the whole scaffold wizard over its own wire format by
implementing Prompter.

src/main.rs

@@ -321,10 +321,14 @@ fn main() {
             // the structural self-checks inside `scaffold` always run), with
             // the scaffold outcome (e.g. a failed vendoring) shaping the
             // offer.
+            let prompter = pkh::ui::prompt::TerminalPrompter;
             if let Err(e) = rt.block_on(async {
-                let opts = pkh::new::questions::run(cli).await?;
+                let opts = pkh::new::questions::run(cli, &prompter).await?;
                 let outcome = pkh::new::scaffold(opts.clone(), &multi)?;
-                pkh::new::questions::offer_verification(&opts, &outcome, &multi, no_verify).await;
+                pkh::new::questions::offer_verification(
+                    &opts, &outcome, &multi, no_verify, &prompter,
+                )
+                .await;
                 Ok::<(), Box<dyn std::error::Error>>(())
             }) {
                 error!("{}", e);