fix: heartbeat button shows proper errors instead of failing silently

- CSRF check returns JSON instead of die() with raw text
- JS parses non-JSON responses gracefully and shows server error
- Visual feedback (check/cross icon) on success/failure
- 3-second icon revert after result

Claude-Session: https://claude.ai/code/session_01Jo2JpjCwfHAh2HHRSjczKq

source/packages/com_mokosuiteclient/admin/src/Controller/DisplayController.php

@@ -85,7 +85,12 @@ class DisplayController extends BaseController
 
 	public function sendHeartbeat()
 	{
-		Session::checkToken() or die(Text::_('JINVALID_TOKEN'));
+		if (!Session::checkToken())
+		{
+			$this->jsonResponse(['success' => false, 'message' => 'Session expired — please reload the page.']);
+
+			return;
+		}
 
 		try
 		{

source/packages/com_mokosuiteclient/media/js/dashboard.js

@@ -126,20 +126,31 @@ document.addEventListener('DOMContentLoaded', function () {
 			fd.append(token, '1');
 
 			fetch(url, {method: 'POST', body: fd, headers: {'X-Requested-With': 'XMLHttpRequest'}})
-				.then(function (r) { return r.json(); })
+				.then(function (r) {
+					return r.text().then(function (text) {
+						try { return JSON.parse(text); }
+						catch (e) { return {success: false, message: 'Server error: ' + text.substring(0, 200)}; }
+					});
+				})
 				.then(function (d) {
+					var msg = d.message || (d.success ? 'Heartbeat sent to HQ.' : 'Heartbeat failed.');
 					if (d.success) {
-						Joomla.renderMessages({message: [d.message || 'Heartbeat sent to HQ.']});
+						if (icon) { icon.className = 'icon-check'; icon.style.color = '#198754'; }
+						Joomla.renderMessages({message: [msg]});
 					} else {
-						Joomla.renderMessages({error: [d.message || 'Heartbeat failed.']});
+						if (icon) { icon.className = 'icon-times'; icon.style.color = '#dc3545'; }
+						Joomla.renderMessages({error: [msg]});
 					}
 				})
-				.catch(function () {
-					Joomla.renderMessages({error: ['Network error sending heartbeat.']});
+				.catch(function (err) {
+					if (icon) { icon.className = 'icon-times'; icon.style.color = '#dc3545'; }
+					Joomla.renderMessages({error: ['Heartbeat failed: ' + (err.message || 'network error')]});
 				})
 				.finally(function () {
 					btn.disabled = false;
-					if (icon) icon.className = 'icon-upload';
+					setTimeout(function () {
+						if (icon) { icon.className = 'icon-upload'; icon.style.color = ''; }
+					}, 3000);
 				});
 		});
 	}