docs(adr): add glossary pages and ADR baseline structure

docs/product-engineering/domain-glossary.md

@@ -0,0 +1,35 @@
+# Domain Glossary
+
+## Core Terms
+
+### Owner
+
+Highest-privilege admin role. Exactly one canonical owner must exist at all times.
+
+### Support User
+
+Hidden technical support account used for break-glass access and operational recovery.
+
+### Admin Registration Policy
+
+Runtime policy controlling whether `/register` can create additional admin users after owner bootstrap.
+
+### Protected Account
+
+Account that cannot be deleted/demoted through self-service flows (support + canonical owner).
+
+### CRUD Service
+
+Shared `@cms/crud` service abstraction combining schema validation, repository orchestration, and audit hooks.
+
+### Permission Scope
+
+RBAC access scope granularity: `own`, `team`, `global`.
+
+### Roadmap Source Of Truth
+
+`TODO.md` in repository root. Rendered in admin via `/todo`.
+
+### Header Banner
+
+Public-site announcement strip configured through `system_setting` key `public.header_banner`.

docs/product-engineering/index.md

@@ -10,8 +10,10 @@ This section covers platform and implementation documentation for engineers and
 - [RBAC And Permissions](/product-engineering/rbac-permission-model)
 - [i18n Conventions](/product-engineering/i18n-conventions)
 - [CRUD Examples](/product-engineering/crud-examples)
+- [Domain Glossary](/product-engineering/domain-glossary)
 - [Environment Runbook](/product-engineering/environment-runbook)
 - [Testing Strategy Baseline](/product-engineering/testing-strategy)
+- [ADR Index](/adr/)
 - [Workflow](/workflow)
 
 ## Scope
@@ -23,6 +25,4 @@ This section covers platform and implementation documentation for engineers and
 
 ## Planned Expansions
 
-- Domain model and glossary
-- ADR (Architecture Decision Record) index
 - Operational playbooks (incident, rollback, recovery)