fix: Fix OPC UA client async security policy setting and handle missing Modbus registers

- OPC UA client: Await set_security_string method call
- Modbus client: Handle case where performance metrics registers might not exist

src/dashboard/protocol_clients.py

@@ -28,7 +28,7 @@ class OPCUAClient:
             # Explicitly set security policy to match server configuration
             # The server supports both Basic256Sha256 and None security policies
             # Use None for development/testing
-            self._client.set_security_string("http://opcfoundation.org/UA/SecurityPolicy#None")
+            await self._client.set_security_string("http://opcfoundation.org/UA/SecurityPolicy#None")
             
             # Set timeout for connection
             await asyncio.wait_for(self._client.connect(), timeout=5.0)
@@ -201,8 +201,13 @@ class ModbusClient:
             # Read safety status - base address 200
             safety_status = self.read_input_register(200 + pump_offset, 1)
             
-            # Read performance metrics - base address 400
+            # Read performance metrics - base address 400 (if available)
+            efficiency = None
+            try:
                 efficiency = self.read_input_register(400 + pump_offset, 1)
+            except Exception:
+                # Performance metrics might not be available
+                pass
             
             return {
                 "setpoint": setpoint[0] if setpoint else None,