Added is_power_strip flag to device_models (schema migration, model,
form checkbox, DB CRUD). Power strip devices in rack view now render
a grid of plug-icon outlets instead of the regular port list, with
custom cable colors showing which outlets are in use.
Extracted shared _port_list.html partial with connected-port checking,
loaded into every page's template set. DeviceView and WallSocket handlers
now load connection data and pass it to the template. Removed duplicate
inline port_list definition from rack.html.