Expose a compact decision trace for skipped or denied jobs

[pilipilisbot]

Context

The bridge records many useful events, but operators need a very fast answer to: why did this notification not dispatch an agent?

Proposal

Add a compact decision trace to job detail and/or dashboard cards: source trust, enabled repo check, action, work intent, decision, route, role, model route, and skip reason.

Acceptance criteria

• Skipped, denied, waiting, and done no-op jobs show a clear “why” summary.
• API returns structured decision trace fields.
• Dashboard renders the trace without requiring log spelunking.

Priority

Low.