fix: correct UTC timestamp display in scan history, pending devices, and detail panel

frontend/src/components/modals/PendingDeviceModal.tsx

@@ -105,7 +105,7 @@ export function PendingDeviceModal({ device, onClose, onApprove, onHide, onIgnor
             {device.discovery_source && (
               <InfoRow label="Source" value={device.discovery_source.toUpperCase()} />
             )}
-            <InfoRow label="Discovered" value={new Date(device.discovered_at).toLocaleString()} />
+            <InfoRow label="Discovered" value={new Date(device.discovered_at.endsWith('Z') ? device.discovered_at : device.discovered_at + 'Z').toLocaleString()} />
           </div>
 
           {/* Services */}

frontend/src/components/panels/DetailPanel.tsx

@@ -147,7 +147,7 @@ export function DetailPanel({ onEdit }: DetailPanelProps) {
         {data.mac && <DetailRow label="MAC" value={data.mac} mono />}
         {data.os && <DetailRow label="OS" value={data.os} />}
         {data.check_method && <DetailRow label="Check" value={data.check_method} mono />}
-        {data.last_seen && <DetailRow label="Last Seen" value={new Date(data.last_seen).toLocaleString()} />}
+        {data.last_seen && <DetailRow label="Last Seen" value={new Date(data.last_seen.endsWith('Z') ? data.last_seen : data.last_seen + 'Z').toLocaleString()} />}
       </div>
 
       {(data.cpu_count != null || data.cpu_model || data.ram_gb != null || data.disk_gb != null) && (

frontend/src/components/panels/Sidebar.tsx

@@ -482,7 +482,7 @@ function ScanHistoryPanel() {
             )}
           </div>
           <div className="text-muted-foreground text-[10px] mt-0.5">
-            {new Date(r.started_at).toLocaleString()}
+            {new Date(r.started_at.endsWith('Z') ? r.started_at : r.started_at + 'Z').toLocaleString()}
           </div>
           {r.ranges.length > 0 && (
             <div className="text-[#8b949e] text-[10px] font-mono truncate">{r.ranges.join(', ')}</div>