INST-9 · Institution/affiliation as a first-class field

> Item derived from the fact-checking cycle analysis (**2026-07-03, v2**). New item (companion proposal **ENG-6**).

### Finding (evidence)
Today only the sparse `nameSpace` tag exists; institutional adoption and per-hub coverage aren't queryable from platform data.

### Action
Promote institution/affiliation to a structured, first-class field on the user/task — **not** derived from namespace.

### Impact
Institutional adoption and per-hub coverage become reportable directly from platform data.

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- **Priority:** 🟡 Medium · **Effort:** M
- **Epic:** #2489