Fix browser client WS connection: missing brace, error handling, localhost fallback

Removing the Enabled else-if branch in a previous commit left the Soll
if-block unclosed, crashing app.js at parse time so no JS ran at all.
Also adds: onerror handler surfaces connection failures in the status
label; try/catch for invalid URL; 'Connecting…' feedback; localhost
fallback when location.hostname is empty (file:// open); wider host
input field.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01DF16nV2ispNw1C9SbvqbRQ

web/app.js

@@ -588,6 +588,7 @@ function onTempCtrlChanged(msg) {
 					initialHeatrateSync = false;
 				}
 			}
+		}
 		if (key === 'Ist') {
 			const ist = msg.Ist;
 			if ('Temp' in ist) {
@@ -726,8 +727,18 @@ function setConnected(isConnected) {
 }
 
 function connect() {
-	const host = document.getElementById('host').value;
-	ws = new WebSocket(host);
+	const statusEl = document.getElementById('conn-status');
+	const url = document.getElementById('host').value.trim();
+	let ws_;
+	try {
+		ws_ = new WebSocket(url);
+	} catch (e) {
+		statusEl.textContent = `Invalid host: ${e.message}`;
+		statusEl.className = 'status-disconnected';
+		return;
+	}
+	ws = ws_;
+	statusEl.textContent = 'Connecting…';
 	ws.onopen = () => {
 		setConnected(true);
 		for (const channel of CHANNELS) {
@@ -739,6 +750,10 @@ function connect() {
 		// (see updateSudForecast()'s isNewSchedule check).
 		sendMsg('Sud', {Save: true});
 	};
+	ws.onerror = () => {
+		statusEl.textContent = `Could not connect to ${url}`;
+		statusEl.className = 'status-disconnected';
+	};
 	ws.onclose = () => setConnected(false);
 	ws.onmessage = (event) => {
 		const msg = JSON.parse(event.data);
@@ -759,7 +774,7 @@ function disconnect() {
 
 // --- DOM wiring. ---
 
-document.getElementById('host').value = `ws://${location.hostname}:8765`;
+document.getElementById('host').value = `ws://${location.hostname || 'localhost'}:8765`;
 
 document.getElementById('btn-connect').addEventListener('click', () => {
 	if (connected) {

web/style.css

@@ -69,6 +69,7 @@ header#connection-bar {
     padding: 0.6em 0;
     border-bottom: 1px solid var(--border);
 }
+#host { width: 18em; }
 
 .status-connected    { color: var(--green); font-weight: bold; }
 .status-disconnected { color: var(--text-muted); }