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.

tests/unit/test_unit_websockets_v3.py

@@ -0,0 +1,74 @@
+import sys
+import os
+import asyncio
+import unittest
+from unittest.mock import MagicMock, AsyncMock, patch
+from datetime import datetime, timezone
+
+# Add project root to path
+sys.path.append(os.getcwd())
+
+# Mock app.config BEFORE imports
+mock_config = MagicMock()
+mock_config.settings = MagicMock()
+mock_config.settings.REDIS = {'server': 'localhost', 'port': 6379}
+sys.modules["app.config"] = mock_config
+
+from app.lib_websockets_v3 import WS_Message_V3, WS_Manager_V3
+
+class TestWSV3Library(unittest.TestCase):
+
+    def test_message_model_validation(self):
+        print("\n--- Testing WS_Message_V3 Validation ---")
+        data = {
+            "msg_type": "cmd",
+            "target": "group",
+            "from_id": "client_abc",
+            "group_id": "group_123",
+            "cmd": "RELOAD",
+            "payload": {"force": True}
+        }
+        msg = WS_Message_V3(**data)
+        self.assertEqual(msg.version, "3")
+        self.assertEqual(msg.cmd, "RELOAD")
+        self.assertTrue(isinstance(msg.sent_at.isoformat(), str))
+        print("✅ Model validation passed.")
+
+    def test_channel_name_generation(self):
+        print("\n--- Testing Channel Name Generation ---")
+        manager = WS_Manager_V3()
+        channels = manager.get_channel_names("client_abc", "group_123")
+        
+        self.assertIn("ws:client:client_abc", channels)
+        self.assertIn("ws:group:group_123", channels)
+        self.assertIn("ws:broadcast", channels)
+        print("✅ Channel name generation passed.")
+
+    @patch('redis.asyncio.Redis.from_url')
+    def test_publish_routing(self, mock_redis_factory):
+        print("\n--- Testing Publish Routing ---")
+        mock_redis = AsyncMock()
+        mock_redis_factory.return_value = mock_redis
+        
+        manager = WS_Manager_V3()
+        
+        async def run_test():
+            # 1. Test Group Routing
+            msg_group = WS_Message_V3(
+                msg_type="msg", target="group", from_id="sender", group_id="target_group"
+            )
+            await manager.publish_message(msg_group)
+            mock_redis.publish.assert_called_with("ws:group:target_group", unittest.mock.ANY)
+            
+            # 2. Test Direct Routing
+            msg_direct = WS_Message_V3(
+                msg_type="msg", target="direct", from_id="sender", to_id="target_client"
+            )
+            await manager.publish_message(msg_direct)
+            mock_redis.publish.assert_called_with("ws:client:target_client", unittest.mock.ANY)
+
+        asyncio.run(run_test())
+        print("✅ Publish routing logic passed.")
+
+if __name__ == "__main__":
+    unittest.main()