feat(debrief): Generate issue previews from action items

[juanRodriguez17]

Description

The /debrief skill presents "Create action item tickets" as a handoff option but marks it as not implemented, leaving users at a dead end after selecting it.

The debrief document already structures action items by category (Prevent / Detect / Respond). Rather than creating issues programmatically — which introduces network side effects and sits outside the skill's documentation-only contract — the skill should render formatted, ready-to-copy issue drafts the user can submit manually.

Requirements

• "Create action item tickets" handoff option is renamed to "Generate issue previews" and is fully functional.
• Each action item in the debrief document produces one preview block containing: title, suggested label (prevent / detect / respond), and a body with debrief context (root cause summary, affected files, relevant commit or PR links).
• All previews are rendered in a single fenced block for easy copying.
• No gh, glab, or any external CLI calls are made — output is display-only.

Additional Context

• Out of scope: programmatic issue creation via CLI (that can be a follow-up once there is appetite to introduce network side effects in the skill).