fix: add defensive optional chaining for node.chip access

Rust DiscoveredNode stub doesn't include chip field yet.
Use optional chaining (node.chip?.toUpperCase()) to prevent
TypeError at runtime.

Co-Authored-By: claude-flow <ruv@ruv.net>

rust-port/wifi-densepose-rs/crates/wifi-densepose-desktop/ui/src/components/NodeCard.tsx

@@ -96,7 +96,7 @@ export function NodeCard({ node, onClick }: NodeCardProps) {
       >
         <DetailRow label="MAC" value={node.mac ?? "--"} mono />
         <DetailRow label="Firmware" value={node.firmware_version ?? "--"} mono />
-        <DetailRow label="Chip" value={node.chip.toUpperCase()} />
+        <DetailRow label="Chip" value={node.chip?.toUpperCase() ?? "--"} />
         <DetailRow label="Role" value={node.mesh_role} />
         <DetailRow
           label="TDM"

rust-port/wifi-densepose-rs/crates/wifi-densepose-desktop/ui/src/pages/Nodes.tsx

@@ -192,7 +192,7 @@ function NodeRow({
         <Td mono>{node.mac ?? "--"}</Td>
         <Td mono>{node.ip}</Td>
         <Td mono>{node.firmware_version ?? "--"}</Td>
-        <Td>{node.chip.toUpperCase()}</Td>
+        <Td>{node.chip?.toUpperCase() ?? "--"}</Td>
         <Td>{formatLastSeen(node.last_seen)}</Td>
       </tr>
       {isExpanded && (