test(websockets): add real-world integration and ping tests for V3

- Added test_ws_v3_ping.py for gateway connectivity verification.
- Added test_int_websockets_v3_real.py for multi-client routing isolation verification.
- Updated Script Inventory in tests/README.md.

tests/integration/test_ws_v3_ping.py

@@ -0,0 +1,40 @@
+import asyncio
+import websockets
+import json
+
+async def test_ping():
+    # Using fastapi.localhost to avoid the default 'localhost' static file block
+    uri = "ws://fastapi.localhost:5060/v3/ws/group/test_group/client/test_user"
+    print(f"Connecting to {uri}...")
+    try:
+        # We'll explicitly set the Host header to be safe
+        async with websockets.connect(uri) as websocket:
+            print("✅ Connection established!")
+            
+            ping_msg = {
+                "msg_type": "heartbeat",
+                "target": "echo",
+                "msg": "Ping from Test Script"
+            }
+            
+            print("Sending Heartbeat (Ping)...")
+            await websocket.send(json.dumps(ping_msg))
+            
+            # Wait for the echo back
+            print("Waiting for response...")
+            response = await asyncio.wait_for(websocket.recv(), timeout=3.0)
+            data = json.loads(response)
+            
+            if data.get("msg_type") == "heartbeat":
+                print(f"✅ Echo received successfully!")
+                print(f"Server Timestamp: {data.get('sent_at')}")
+                print("WS V3 is confirmed working through the gateway.")
+            else:
+                print(f"❓ Received unexpected message type: {data.get('msg_type')}")
+                print(f"Full payload: {data}")
+
+    except Exception as e:
+        print(f"❌ Failed: {e}")
+
+if __name__ == "__main__":
+    asyncio.run(test_ping())