Default to the same host when determing WebSocket URL

We still need to be able to override it in order to use the Sveltekit dev server

webif/src/lib/websocket.ts

@@ -0,0 +1,9 @@
+export const determineWebSocketUrl = () => {
+  const urlParams = new URLSearchParams(window.location.search)
+
+  // Use whatever is specified by the "ws" query parameter, default
+  // to the current host of nothing is specified. This allows us to
+  // manually define the WebSocket host when running the Svelte
+  // development server.
+  return urlParams.get('ws') || `ws://${window.location.host}`
+}

webif/src/routes/+page.svelte

@@ -1,5 +1,7 @@
 <script>
   import { onMount } from 'svelte'
+  import { determineWebSocketUrl } from '$lib/websocket'
+
   import Logo from './Logo.svelte'
   import Configuration from './Configuration.svelte'
   import LastUpdate from './LastUpdate.svelte'
@@ -14,12 +16,6 @@
   let mainsSensorData
   let circuitSensorData
 
-  const determineWebSocketUrl = () => {
-    const urlParams = new URLSearchParams(window.location.search)
-
-    return urlParams.get('ws') || undefined
-  }
-
   const parseTimestamp = (sensorData) => {
     return new Date(sensorData[0].timestamp)
   }