phase 2 (part 1): OpenAPI-generated API server, first 9 endpoints

- api/openapi.yaml converted 3.1 → 3.0.3 (oapi-codegen/kin-openapi
  supports 3.0; nullable syntax + example keywords), still redocly-clean
- oapi-codegen (v2.4.1, strict server + chi) generates
  internal/httpapi/gen from the spec; `make generate` wired
- internal/httpapi: chi router, /healthz (unauthenticated, SG18),
  RFC 9457 problem+json mapping from domain sentinels (SG11), 5xx detail
  logged server-side only, request logging with request IDs, graceful
  shutdown (SG4), interim static bearer auth (constant-time; dev-open
  when no token; OIDC JWT still to come in Phase 2)
- Implemented: listEntities (type filter walks the hierarchy, keyset
  pagination), getEntity (UUID or slug, ETag), getEntityRelations,
  getBlastRadius, getGraph (nodes+edges for UIs), getOntology,
  listSignals, getFleetHealth, exportSeeds. Remaining 38 ops return 501
  problem+json stubs (compiler-enforced interface completeness)
- `oikos api` role live: migrate-on-start, serves :8090
- 15 API integration tests (auth, pagination, hierarchy filter, ETag,
  404/501 problem shapes, graph, export)

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Makefile

@@ -14,14 +14,15 @@ test-db:
 	docker compose up -d postgres
 	@sleep 3
 	OIKOS_TEST_DATABASE_URL="postgres://oikos:$${OIKOS_DB_PASSWORD:-oikos_dev}@localhost:5432/oikos?sslmode=disable" \
-		$(GO) test -race -count=1 ./internal/db/
+		$(GO) test -race -count=1 ./internal/db/ ./internal/httpapi/
 
 lint:
 	$(GO) vet ./...
 	@command -v golangci-lint >/dev/null 2>&1 && golangci-lint run || echo "golangci-lint not installed, skipping"
 
 generate:
-	@echo "TODO: oapi-codegen + sqlc generation"
+	$(GO) run github.com/oapi-codegen/oapi-codegen/v2/cmd/oapi-codegen@v2.4.1 \
+		-config api/codegen.yaml api/openapi.yaml
 
 migrate:
 	$(GO) run ./cmd/oikos migrate