feat(websockets): implement WebSockets V3 with granular Redis Pub/Sub

- Introduced WS_Message_V3 standardized Pydantic model and WS_Manager_V3.
- Implemented /v3/ws/ endpoint with granular Redis routing to solve "noisy neighbor" scaling issues.
- Added presence tracking using Redis Sets for group coordination.
- Comprehensive test suite added (unit and integration) covering models, manager, and routing logic.
- Documentation: Created V3 Frontend WebSocket Guide and Project design spec.
- Updated main Frontend API guide and tests README with new standards.

documentation/GUIDE__V3_FRONTEND_API.md

@@ -128,7 +128,17 @@ V3 uses a **String-Only ID Vision**. The frontend NEVER handles or stores databa
 
 ---
 
-## 7. Structured Error Handling
+## 9. Real-Time Communication (V3 WebSockets)
+
+V3 WebSockets provide a granular, high-performance messaging layer.
+
+- **Guide**: [Aether API V3 WebSocket Integration Guide](./GUIDE__V3_FRONTEND_WEBSOCKETS.md)
+- **Endpoint**: `ws://[api_domain]/v3/ws/group/{group_id}/client/{client_id}`
+- **Key Requirement**: All messages must conform to the `WS_Message_V3` schema.
+
+---
+
+## 10. Structured Error Handling
 
 V3 returns machine-readable error objects in `meta.details` for failures.