Replace polling with websocket live sync

src/SystemTab.tsx

@@ -1,4 +1,4 @@
-import { FormEvent, useEffect, useMemo, useState } from 'react';
+import { FormEvent, useEffect, useMemo, useRef, useState } from 'react';
 import type { DashboardSnapshot, ProxyServiceRecord, SystemSettings, UpdateSystemInput } from './shared/contracts';
 import type { PanelLanguage, PanelPreferences, PanelTheme } from './lib/panelPreferences';
 import { getPanelText, getThemeLabel } from './lib/panelText';
@@ -21,12 +21,25 @@ export default function SystemTab({
   const [error, setError] = useState('');
   const [isSaving, setIsSaving] = useState(false);
   const [removeServiceId, setRemoveServiceId] = useState<string | null>(null);
+  const lastAppliedSystemKey = useRef(serializeSystemSettings(cloneSystemSettings(snapshot.system)));
   const text = getPanelText(preferences.language);
 
   useEffect(() => {
-    setDraft(cloneSystemSettings(snapshot.system));
-    setError('');
-  }, [snapshot.system]);
+    const incomingDraft = cloneSystemSettings(snapshot.system);
+    const incomingKey = serializeSystemSettings(incomingDraft);
+    const draftKey = serializeSystemSettings(draft);
+
+    if (incomingKey === lastAppliedSystemKey.current) {
+      return;
+    }
+
+    if (draftKey === lastAppliedSystemKey.current || draftKey === incomingKey) {
+      setDraft(incomingDraft);
+      setError('');
+    }
+
+    lastAppliedSystemKey.current = incomingKey;
+  }, [draft, snapshot.system]);
 
   const linkedUsersByService = useMemo(() => {
     const result = new Map<string, string[]>();
@@ -249,6 +262,7 @@ export default function SystemTab({
                 className="button-secondary"
                 onClick={() => {
                   setDraft(cloneSystemSettings(snapshot.system));
+                  lastAppliedSystemKey.current = serializeSystemSettings(cloneSystemSettings(snapshot.system));
                   setError('');
                 }}
               >
@@ -344,3 +358,7 @@ function createServiceDraft(existingServices: ProxyServiceRecord[]): ProxyServic
     assignable: true,
   };
 }
+
+function serializeSystemSettings(system: UpdateSystemInput): string {
+  return JSON.stringify(system);
+}