adr: ADR-0001 engine activation via feature-control (OpenFeature, availability-only)

Records the accepted decision: shard-wiki's native engine uses feature-control via
OpenFeature for per-shard extension activation (availability only, never authz),
provider-pluggable with a LocalProvider standalone default (mirrors the identity
ladder), at the engine layer, consuming the mature feature-control.evaluate slice.
Adds spec/adr/ series + README; hub decision abf7830f recorded.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

spec/README.md

@@ -9,6 +9,7 @@ Background on document types: InfoTechPrimers on coulomb.social.
 | `CoreArchitectureBlueprint.md` | draft for review | **Whole-system architecture** — layers, abstractions, load-bearing decisions (synthesised from all research) |
 | `FederationArchitecture.md` | draft for review | federation design — *what the union does*: T1–T10 decision records + the federation-model taxonomy (SHARD-WP-0002) |
 | `WikiEngineCoreArchitecture.md` | draft for review | the native **headless, API-first wiki engine** — small page-store kernel + typed-extension framework, as a canonical-mode shard backend (SHARD-WP-0013) |
+| `adr/` | living | Architecture Decision Records (ADR-0001: engine activation via feature-control) |
 | `FederationRequirements.md` | draft for review | yawex-derived union/federation design notes — resolution, namespace, derived views, provenance, overlay, links (ADR-01…06; SHARD-WP-0001) |
 | `ProductRequirementsDocument.md` | draft scaffold | What the product must deliver |
 | `TechnicalSpecificationDocument.md` | draft + §A | How the system is built; **§A = the normative shard adapter contract** (T11–T16, T18; SHARD-WP-0002) |