Persist one browser user agent for Axios and WebSockets

app/settings/page.tsx

@@ -47,6 +47,7 @@ interface AppSettings {
     trading_hours: string | null;
     master_backup_token: string | null;
     proxy_url: string | null;
+    user_agent: string | null;
     backup_last_push_at: string | null;
     backup_last_error: string | null;
 }
@@ -77,6 +78,7 @@ export default function SettingsPage() {
     const [saved, setSaved] = useState(false);
     const [backupToken, setBackupToken] = useState<string>('');
     const [proxyUrl, setProxyUrl] = useState<string>('');
+    const [userAgent, setUserAgent] = useState<string>('');
     const [backupStatus, setBackupStatus] = useState<{ at: string | null; error: string | null }>({ at: null, error: null });
     const [restoreList, setRestoreList] = useState<BackupMeta[] | null>(null);
     const [restoreBusy, setRestoreBusy] = useState(false);
@@ -130,6 +132,7 @@ export default function SettingsPage() {
                 if (s.proxy_url != null) {
                     setProxyUrl(s.proxy_url);
                 }
+                setUserAgent(s.user_agent ?? '');
                 setBackupStatus({ at: s.backup_last_push_at, error: s.backup_last_error || null });
             });
 
@@ -440,6 +443,16 @@ export default function SettingsPage() {
                             className="w-72 rounded-lg border border-slate-200 bg-slate-50 px-3 py-1.5 text-sm font-mono text-slate-800 focus:outline-none focus:ring-2 focus:ring-blue-500"
                         />
                     </div>
+                    <div className="border-t border-slate-100 px-4 py-3">
+                        <p className="text-sm font-medium text-slate-800">User agent</p>
+                        <p className="text-xs text-slate-400 mt-0.5">
+                            Chrome, Firefox, or Edge is randomly selected on first load and saved.
+                            All server Axios requests and WebSocket connections reuse it, including after restarts.
+                        </p>
+                        <p className="mt-2 break-all rounded-lg bg-slate-50 px-3 py-2 text-xs font-mono text-slate-700">
+                            {userAgent || 'Loading…'}
+                        </p>
+                    </div>
                 </div>
 
                 {/* ── Instruments ── */}