[frontend-contrib S22] Sagas/triggers/streams dashboard-zone panels

[rickylabs]

Part of #922

Scope

Complete the four first-party capability panels on app.dashboard.panels (workers ships in the dogfood slice): sagas, triggers, streams — the panel set the dashboard epic (#400) consumes in the same cut.

Design source: RFC #890 (rfc.md §5) + .llm/runs/plan-frontend-contrib--seed/design/canonical/ (rev 3).

Acceptance

• gate: all four panels render + hydrate in one scaffolded app (scaffold.runtime extension)