fix: address Plan 2 final-review findings

- tui/doc.go: remove teatest blank import (test harness in prod binary)
- cmd: honor wizard HaltOnError toggle in addition to --halt-on-error flag
- cmd: wire SIGINT/SIGTERM to root context via signal.NotifyContext
- dashboard/run: derive engine context and cancel on tea.Program exit
  so the engine goroutine does not outlive Run

cmd/archduino/main.go

@@ -4,6 +4,8 @@ import (
 	"context"
 	"fmt"
 	"os"
+	"os/signal"
+	"syscall"
 	"time"
 
 	"github.com/spf13/cobra"
@@ -41,7 +43,13 @@ func main() {
 		Version:       version,
 	}
 	root.AddCommand(newInstallCmd())
-	if err := root.Execute(); err != nil {
+
+	// Wire SIGINT/SIGTERM to a cancellable context so long-running phases
+	// (engine.Run, sudo keepalive) observe the cancellation promptly.
+	ctx, stop := signal.NotifyContext(context.Background(), os.Interrupt, syscall.SIGTERM)
+	defer stop()
+
+	if err := root.ExecuteContext(ctx); err != nil {
 		fmt.Fprintln(os.Stderr, "error:", err)
 		os.Exit(1)
 	}
@@ -140,7 +148,8 @@ func newInstallCmd() *cobra.Command {
 					fmt.Fprintln(os.Stdout, "installation cancelled")
 					return nil
 				}
-				sum, runErr = dashboard.Run(ctx, Registry, finalState, halt)
+				// Either the CLI flag or the wizard toggle can force halt-on-error.
+				sum, runErr = dashboard.Run(ctx, Registry, finalState, halt || finalState.HaltOnError)
 			}
 
 			ended := time.Now().UTC()