docs: Align documentation with true microservices architecture

Transform all documentation from modular monolith to true microservices
architecture where core services are independently deployable.

Key Changes:
- Core Kernel: Infrastructure only (no business logic)
- Core Services: Auth, Identity, Authz, Audit as separate microservices
  - Each service has own entry point (cmd/{service}/)
  - Each service has own gRPC server and database schema
  - Services register with Consul for service discovery
- API Gateway: Moved from Epic 8 to Epic 1 as core infrastructure
  - Single entry point for all external traffic
  - Handles routing, JWT validation, rate limiting, CORS
- Service Discovery: Consul as primary mechanism (ADR-0033)
- Database Pattern: Per-service connections with schema isolation

Documentation Updates:
- Updated all 9 architecture documents
- Updated 4 ADRs and created 2 new ADRs (API Gateway, Service Discovery)
- Rewrote Epic 1: Core Kernel & Infrastructure (infrastructure only)
- Rewrote Epic 2: Core Services (Auth, Identity, Authz, Audit as services)
- Updated Epic 3-8 stories for service architecture
- Updated plan.md, playbook.md, requirements.md, index.md
- Updated all epic READMEs and story files

New ADRs:
- ADR-0032: API Gateway Strategy
- ADR-0033: Service Discovery Implementation (Consul)

New Stories:
- Epic 1.7: Service Client Interfaces
- Epic 1.8: API Gateway Implementation

docs/content/stories/epic8/README.md

@@ -1,7 +1,9 @@
 # Epic 8: Advanced Features & Polish
 
 ## Overview
-Add advanced features (OIDC, GraphQL, API Gateway), performance optimization, additional sample modules, and final polish and bug fixes.
+Add advanced features (OIDC, GraphQL), performance optimization, additional sample feature services, and final polish and bug fixes.
+
+**Note:** API Gateway is now in Epic 1 (Story 1.8) as core infrastructure, not an advanced feature.
 
 ## Stories
 
@@ -15,10 +17,10 @@ Add advanced features (OIDC, GraphQL, API Gateway), performance optimization, ad
 - **Goal:** Add optional GraphQL API alongside REST API.
 - **Deliverables:** GraphQL schema, resolvers, GraphQL endpoint
 
-### 8.3 Additional Sample Modules
-- [Story: 8.3 - Additional Modules](./8.3-additional-modules.md)
-- **Goal:** Create additional sample modules to demonstrate different use cases.
-- **Deliverables:** Notification module, Analytics module
+### 8.3 Additional Sample Feature Services
+- [Story: 8.3 - Additional Services](./8.3-additional-modules.md)
+- **Goal:** Create additional sample feature services to demonstrate different use cases and patterns.
+- **Deliverables:** Notification Service, Analytics Service (as independent services with their own entry points)
 
 ### 8.4 Final Polish and Optimization
 - [Story: 8.4 - Final Polish](./8.4-final-polish.md)