INST-4 · Explicit lifecycle state + abandoned/archived

> Item derived from the fact-checking cycle analysis (**2026-07-03, v2**). Refined with backlog decomposition. Absorbs companion **ENG-3 + OPS-2**.

### Finding (refined, verified)
The ~215 open tasks are **not a single block**:
- **~60–75 abandoned** — empty `reviewData`, idle **~590–660 d**
- **~142–155 stuck-active** — have content, idle **~226–235 d**

*Nuance:* in `main` only, the stuck-active drop to **~108 → ~70 d** — the old passive backlog is mostly workshop/test.

### Action
- `lifecycle.status` (draft / in_progress / published / rejected / **abandoned** / **archived**)
- `isOpen`
- `lastActivityAt`
- Daily job that marks `abandoned` by empty `reviewData` **or** N days without activity.

### Impact
The live backlog becomes truly measurable; separates a healthy queue from dead liabilities. Enables the split governance work: PROC-2a (purge/diagnose abandoned) and PROC-2b (triage/SLA stuck-active).

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- **Priority:** 🔴 High · **Effort:** P/M
- **Dependencies:** requires migration/backfill (`needs-migration`). Wave 2, alongside INST-2 (#2492).
- **Epic:** #2489