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/architecture/data-flow-patterns.md

@@ -19,18 +19,22 @@ Data flows through the platform in multiple patterns depending on the type of op
 
 ### Standard HTTP Request Flow
 
-Complete data flow from HTTP request to response.
+Complete data flow from HTTP request through API Gateway to backend service and response.
 
 ```mermaid
 graph TD
-    Start[HTTP Request] --> Auth[Authentication]
-    Auth -->|Valid| Authz[Authorization]
-    Auth -->|Invalid| Error1[401 Response]
+    Start[HTTP Request] --> Gateway[API Gateway]
+    Gateway --> RateLimit{Rate Limit Check}
+    RateLimit -->|Allowed| Auth[Validate JWT via Auth Service]
+    RateLimit -->|Exceeded| Error0[429 Too Many Requests]
     
-    Authz -->|Authorized| Handler[Request Handler]
-    Authz -->|Unauthorized| Error2[403 Response]
+    Auth -->|Valid| Authz[Check Permission via Authz Service]
+    Auth -->|Invalid| Error1[401 Unauthorized]
     
-    Handler --> Service[Domain Service]
+    Authz -->|Authorized| Route[Route to Backend Service]
+    Authz -->|Unauthorized| Error2[403 Forbidden]
+    
+    Route --> Service[Backend Service]
     Service --> Cache{Cache Check}
     
     Cache -->|Hit| CacheData[Return Cached Data]
@@ -42,17 +46,19 @@ graph TD
     Service --> CacheStore[Update Cache]
     
     Service --> EventBus[Publish Events]
-    Service --> Audit[Audit Log]
+    Service --> AuditSvc[Audit Service<br/>gRPC]
     Service --> Metrics[Update Metrics]
     
-    Service --> Handler
-    Handler --> Response[HTTP Response]
-    CacheData --> Response
+    Service --> Gateway
+    Gateway --> Response[HTTP Response]
+    CacheData --> Gateway
+    Error0 --> Response
     Error1 --> Response
     Error2 --> Response
     
     Response --> Client[Client]
     
+    style Gateway fill:#4a90e2,stroke:#2e5c8a,stroke-width:3px,color:#fff
     style Auth fill:#ff6b6b,stroke:#c92a2a,stroke-width:2px,color:#fff
     style Service fill:#50c878,stroke:#2e7d4e,stroke-width:2px,color:#fff
     style Cache fill:#4a90e2,stroke:#2e5c8a,stroke-width:2px,color:#fff
@@ -60,22 +66,30 @@ graph TD
 
 ### Request Data Transformation
 
-How request data is transformed as it flows through the system.
+How request data is transformed as it flows through API Gateway to backend service.
 
 ```mermaid
 sequenceDiagram
     participant Client
-    participant Handler
+    participant Gateway
+    participant BackendService
     participant Service
     participant Repo
     participant DB
     
-    Client->>Handler: HTTP Request (JSON)
-    Handler->>Handler: Parse JSON
-    Handler->>Handler: Validate request
-    Handler->>Handler: Convert to DTO
+    Client->>Gateway: HTTP Request (JSON)
+    Gateway->>Gateway: Rate limiting
+    Gateway->>Gateway: Validate JWT (via Auth Service)
+    Gateway->>Gateway: Check permission (via Authz Service)
+    Gateway->>Gateway: Route to service (via service discovery)
+    Gateway->>Gateway: Forward request (gRPC/HTTP)
     
-    Handler->>Service: Business DTO
+    Gateway->>BackendService: Request (gRPC/HTTP)
+    BackendService->>BackendService: Parse request
+    BackendService->>BackendService: Validate request
+    BackendService->>BackendService: Convert to DTO
+    
+    BackendService->>Service: Business DTO
     Service->>Service: Business logic
     Service->>Service: Domain entity
     
@@ -89,10 +103,13 @@ sequenceDiagram
     
     Service->>Service: Business logic
     Service->>Service: Response DTO
-    Service-->>Handler: Response DTO
+    Service-->>BackendService: Response DTO
     
-    Handler->>Handler: Convert to JSON
-    Handler-->>Client: HTTP Response (JSON)
+    BackendService->>BackendService: Convert to response format
+    BackendService-->>Gateway: Response (gRPC/HTTP)
+    
+    Gateway->>Gateway: Transform response (if needed)
+    Gateway-->>Client: HTTP Response (JSON)
 ```
 
 ## Event Data Flow