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/adr/0031-service-repository-structure.md

@@ -30,12 +30,13 @@ Use a **monorepo structure with service directories** for all services:
    ```
    goplt/
    ├── cmd/
-   │   ├── platform/          # Core kernel entry point
-   │   ├── auth-service/      # Auth Service entry point
-   │   ├── identity-service/  # Identity Service entry point
-   │   ├── authz-service/     # Authz Service entry point
-   │   ├── audit-service/     # Audit Service entry point
-   │   └── blog-service/      # Blog module service entry point
+   │   ├── platform/          # Core kernel entry point (minimal, infrastructure only)
+   │   ├── api-gateway/        # API Gateway service entry point
+   │   ├── auth-service/       # Auth Service entry point
+   │   ├── identity-service/   # Identity Service entry point
+   │   ├── authz-service/      # Authz Service entry point
+   │   ├── audit-service/      # Audit Service entry point
+   │   └── blog-service/       # Blog feature service entry point
    ├── services/              # Service implementations (optional alternative)
    │   ├── auth/
    │   │   ├── internal/      # Service implementation
@@ -145,17 +146,22 @@ Use a **monorepo structure with service directories** for all services:
 - Single entry point `cmd/platform/`
 - Shared infrastructure established
 
-### Phase 2: Service Structure (Epic 2)
-- Create service directories in `cmd/`:
-  - `cmd/auth-service/`
-  - `cmd/identity-service/`
-  - `cmd/authz-service/`
-  - `cmd/audit-service/`
+### Phase 2: Service Structure (Epic 1-2)
+- **Epic 1**: Create API Gateway service:
+  - `cmd/api-gateway/` - API Gateway entry point
+  - Service discovery integration
+  - Request routing to backend services
+- **Epic 2**: Create core service directories:
+  - `cmd/auth-service/` - Auth Service entry point
+  - `cmd/identity-service/` - Identity Service entry point
+  - `cmd/authz-service/` - Authz Service entry point
+  - `cmd/audit-service/` - Audit Service entry point
 - Create service implementations:
-  - Option A: `services/{service}/internal/` for each service
-  - Option B: `internal/{service}/` for each service (if keeping all in internal/)
-  - Option C: Service code directly in `cmd/{service}/` for simple services
-- Define service client interfaces in `pkg/services/`
+  - Option A: `services/{service}/internal/` for each service (recommended)
+  - Option B: `internal/{service}/` for each service
+  - Each service has its own database connection pool
+- Define service client interfaces in `pkg/services/`:
+  - `AuthServiceClient`, `IdentityServiceClient`, `AuthzServiceClient`, `AuditServiceClient`
 - Implement gRPC/HTTP clients in `internal/services/`
 
 ### Phase 3: Module Services (Epic 4+)
@@ -170,18 +176,27 @@ Use a **monorepo structure with service directories** for all services:
 ```
 goplt/
 ├── cmd/
-│   ├── platform/          # Core kernel
+│   ├── platform/          # Core kernel (minimal, infrastructure only)
+│   ├── api-gateway/       # API Gateway entry point
 │   ├── auth-service/      # Auth entry point
 │   ├── identity-service/  # Identity entry point
-│   └── ...
+│   ├── authz-service/     # Authz entry point
+│   ├── audit-service/     # Audit entry point
+│   └── blog-service/      # Blog feature service entry point
 ├── services/              # Service implementations
+│   ├── gateway/
+│   │   ├── internal/      # Gateway implementation
+│   │   └── api/           # Routing logic
 │   ├── auth/
 │   │   ├── internal/      # Service implementation
 │   │   └── api/           # gRPC/HTTP definitions
-│   └── ...
-├── internal/              # Core kernel (shared)
+│   ├── identity/
+│   ├── authz/
+│   ├── audit/
+│   └── blog/
+├── internal/              # Core kernel (shared infrastructure)
 ├── pkg/                   # Public interfaces
-└── modules/               # Feature modules
+└── modules/               # Feature modules (optional structure)
 ```
 
 This provides: