feature/dns rack gateway modal
- Device page links back to its own rack; pad the racks page's tables
- Add device_status_cache storage for the rack-devices page's status column
- Fetch rack u_height and each device's numeric rack unit
- Rack devices page: status column + filter, and a show-empty-units toggle
- Add interface_gateway_choice storage for staged gateway edits
- Add FindOrCreateIPAddress and SetInterfaceGatewayIPs to the NetBox client
- Diff a staged gateway edit into ActionSetGateways; warn on network mismatch
- Apply ActionSetGateways: resolve staged addresses, PATCH gateway_ips
- Device page: gateway chips per interface, add/remove/revert like the rest
- Fix 404 on gateway chip delete: wrong template context for interface id
- Add apply.TouchesNetBox, classifying which action kinds write NetBox
- Confirm NetBox-side changes in a modal before Apply submits