recipe-run preview hold should support failed or in-progress workflows for debugging

## Problem

`wp-codebox recipe-run --preview-hold --preview-hold-blocking` is useful for opening a live Playground preview. Today the preview is effectively tied to successful recipe completion: if a workflow step fails or a long proof never reaches the terminal hold phase, the runtime is torn down and callers cannot inspect the live page/editor that failed.

For generic browser/runtime workflows, callers need a way to hold the preview when a workflow fails or while a long workflow is blocked, without pretending the proof succeeded.

## Evidence

While proving a WPCOM selected-page edit/save/export workflow, WP Codebox could emit a local/public preview URL after the early browser proof, but subsequent workflow failure caused the runtime to be destroyed before a human could inspect the editor state. This is a generic lifecycle problem: preview hold should be a debugging/inspection mode, not a success-only artifact.

## Desired behavior

Add a generic preview-hold failure policy, for example:

- `--preview-hold-on-failure`
- or `--preview-hold-policy=success|failure|always`

The runtime should remain held for the configured hold period or blocking session even if a workflow step fails, while preserving the run status as failed.

## Acceptance criteria

- A failed recipe can still emit `preview.localUrl`/`preview.publicUrl` when preview hold-on-failure is requested.
- Run status remains failed; holding a preview must not mask proof failure.
- Artifacts record failure status and preview lifecycle separately.
- Existing success-only behavior remains the default unless the new option is supplied.
- No WPCOM-specific logic or fixtures.

Beginne damit, den Einstiegspunkt `wp-codebox recipe-run --preview-hold --preview-hold-blocking` durch die Verarbeitung des Vorschaulebenszyklus, den Ausführungsstatus und die Artefaktaufzeichnung zu verfolgen. Überprüfe, wie fehlgeschlagene Schritte derzeit die Laufzeitumgebung abbauen und wie das Halten nur bei Erfolg ausgewählt wird. Erledigt ist dies, wenn die angeforderte Fehlerbehandlung die Laufzeitumgebung hält und Vorschau-URLs ausgibt, während der Status „fehlgeschlagen“ und separate Lebenszyklusartefakte erhalten bleiben und die bestehenden Standardwerte unverändert bleiben.

Vom Indexierungsmodell aus dem Issue-Text verfasst.