fix: Add connection lost indicator to Hosts page

Hosts page now shows a clear error state when WebSocket connection
is lost, with a manual "Reconnect now" button. Also improved loading
state logic to differentiate between initial loading and connection
loss after having received data.

This completes the connection lost UX consistency across all major
pages: Dashboard, Storage, Backups, Replication, and now Hosts.

frontend-modern/src/components/Hosts/HostsOverview.tsx

@@ -83,9 +83,11 @@ export const HostsOverview: Component<HostsOverviewProps> = (props) => {
 
   const connected = () => wsContext.connected();
   const reconnecting = () => wsContext.reconnecting();
+  const reconnect = () => wsContext.reconnect();
 
-  const isLoading = createMemo(() => {
-    return !connected() && !reconnecting();
+  const isInitialLoading = createMemo(() => {
+    // Only show loading spinner when we've never been connected and have no hosts
+    return !connected() && !reconnecting() && props.hosts.length === 0;
   });
 
   const sortedHosts = createMemo(() => {
@@ -194,7 +196,7 @@ export const HostsOverview: Component<HostsOverviewProps> = (props) => {
 
   return (
     <div class="space-y-4">
-      <Show when={isLoading()}>
+      <Show when={isInitialLoading()}>
         <Card padding="lg">
           <EmptyState
             icon={
@@ -219,19 +221,53 @@ export const HostsOverview: Component<HostsOverviewProps> = (props) => {
                 />
               </svg>
             }
-            title={reconnecting() ? 'Reconnecting to host agents...' : 'Loading host data...'}
+            title="Loading host data..."
+            description="Connecting to the monitoring service."
+          />
+        </Card>
+      </Show>
+
+      {/* Disconnected State */}
+      <Show when={!connected() && !isInitialLoading()}>
+        <Card padding="lg" tone="danger">
+          <EmptyState
+            icon={
+              <svg
+                class="h-12 w-12 text-red-400"
+                fill="none"
+                viewBox="0 0 24 24"
+                stroke="currentColor"
+              >
+                <path
+                  stroke-linecap="round"
+                  stroke-linejoin="round"
+                  stroke-width="2"
+                  d="M12 8v4m0 4h.01M21 12a9 9 0 11-18 0 9 9 0 0118 0z"
+                />
+              </svg>
+            }
+            title="Connection lost"
             description={
               reconnecting()
-                ? 'Re-establishing metrics from the monitoring service.'
-                : connected()
-                  ? 'Waiting for the first host update.'
-                  : 'Connecting to the monitoring service.'
+                ? 'Attempting to reconnect…'
+                : 'Unable to connect to the backend server'
+            }
+            tone="danger"
+            actions={
+              !reconnecting() ? (
+                <button
+                  onClick={() => reconnect()}
+                  class="mt-2 inline-flex items-center px-4 py-2 text-xs font-medium rounded bg-red-600 text-white hover:bg-red-700 transition-colors"
+                >
+                  Reconnect now
+                </button>
+              ) : undefined
             }
           />
         </Card>
       </Show>
 
-      <Show when={!isLoading()}>
+      <Show when={!isInitialLoading()}>
         <Show
           when={sortedHosts().length === 0}
           fallback={