[NX-103 Issue] Add offline state handling for unreachable targets

Introduced a mechanism to detect and handle when a target is unreachable, including a detailed offline state message with host and port information. Updated the UI to display a card notifying users of the target's offline status and styled the card accordingly in CSS.

frontend/src/styles.css

@@ -2022,6 +2022,29 @@ select:-webkit-autofill {
   font-size: 12px;
 }
 
+.target-offline-card {
+  border-color: #a85757;
+  background: linear-gradient(130deg, #2c1724 0%, #1f1f38 100%);
+}
+
+.target-offline-card h3 {
+  margin: 0 0 8px;
+  color: #fecaca;
+}
+
+.target-offline-card p {
+  margin: 0 0 10px;
+  color: #fde2e2;
+}
+
+.target-offline-meta {
+  display: flex;
+  flex-wrap: wrap;
+  gap: 16px;
+  font-size: 12px;
+  color: #d4d4f5;
+}
+
 .chart-tooltip {
   background: #0f1934ee;
   border: 1px solid #2f4a8b;