feat(api,ui): showcase-completion E2 — safe replay & workspace lifecycle (confirm/diff, lineage, rename/archive/pin/tags, search, compare, link health)

[w7-mgfcode]

Sub-issue of #406 (umbrella: showcase workspace completion — the forecastlab control story). Parallel after Foundation (E1 #407).

Purpose

Safe replay & workspace lifecycle UI: an explicit confirmation step before any reset=true replay (with destructive copy), a replay preview/diff panel (recorded config vs the request about to be sent), lineage rendering (replayed_from chain + replay-created badge + original-workspace link), and full lifecycle management on the saved-workspaces panel — rename, archive, pin, notes, tags, list search/filter/sort, multi-select delete (metadata-only singles, vision-compatible), and a two-workspace compare view. Folds in the novel ops slice: artifact-link liveness checks with dead-link warnings on soft references and a per-workspace health summary (partial-run warning included).

Sub-tasks

To be decomposed via issue-to-subtasks when this epic is picked up.

[w7-mgfcode]

Delivered by #415 (merged to dev at 0708d7d). Full epic scope shipped: replay confirmation with recorded-vs-sent preview (destructive variant on reset=true), lineage badge + ancestor chain rendering, lifecycle panel (rename/notes/tags/pin/archive/search/filter/sort, archived hidden by default, pinned-first), multi-select delete (N single DELETEs — no bulk endpoint), /showcase/compare two-workspace page, and the GET /demo/workspaces/{id}/health soft-reference probe with dead-link warnings + partial-run chip. Replay-policy picker deliberately deferred per the PRP's Decision 1. CONTRACT(E1) reconciled with zero divergence.