docs(structure): add requirements contract, job namespaces, and enforcement gate

Phase 1 scaffold for the docs consolidation:

- docs/STRUCTURE.md: artifact registry, 8 owner-job ID namespaces, routing and change rules
- docs/REQUIREMENTS.md, docs/MILESTONES.md: normative schema, empty pending Phase 2 port
- docs/_templates/: requirement-row, capability, contract, adr
- docs/capabilities/, docs/contracts/: registered homes
- tools/check_requirements.py: enforces registry, IDs, and traceability
- AGENTS.md: coding paused banner + structure-contract routing rule
- README.md: pointers to the structure/requirements/milestones set

Additive only: no doc moves, no requirement text, no CI wiring yet.

README.md

@@ -7,11 +7,14 @@ Start at [`docs/README.md`](docs/README.md) for goals, what already shipped, and
 | Artifact | File |
 |---|---|
 | Docs map | `docs/README.md` |
+| Structure contract | `docs/STRUCTURE.md` |
+| Requirements (normative) | `docs/REQUIREMENTS.md` |
+| Milestones (ID subsets) | `docs/MILESTONES.md` |
 | Product overview | `docs/PRODUCT.md` |
 | Invariants and agent context | `AGENTS.md` |
 | Milestone 1 Capture (shipped) | `docs/CAPTURE.md` |
 | Milestone 2 Photos (shipped) | `docs/PHOTOS.md` |
-| Milestone 3 Create (current) | `docs/CREATE.md` |
+| Milestone 3 Create (paused — requirements reconciliation) | `docs/CREATE.md` |
 | UAT practice walk | `docs/UAT-PRACTICE.md` |
 | Hosting | `deploy/` |