PROC-2a · Purge/diagnose the ~60–75 abandoned tasks

> Item derived from the fact-checking cycle analysis (**2026-07-03, v2**). Split from PROC-2 (#2500). Absorbs companion **OPS-2**.

### Finding (evidence)
The ~215 open tasks are **not one block**. This item covers the **~60–75 abandoned** ones: empty `reviewData`, idle **~590–660 days**. Nuance: in `main` only, the old passive backlog is mostly workshop/test.

### Action
Archive them **by design** (depends on the `abandoned` state from INST-4 #2494) and **diagnose the intake/assignment cause** that generates them.

### Impact
Clean WIP baseline; the failure mode that produces abandoned tasks is identified.

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- **Priority:** 🔴 High
- **Dependencies:** INST-4 (#2494).
- **Parent:** #2500 · **Epic:** #2490