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.
Added toggleRackHeight() to show/hide the height-in-units field when the
rack-mountable checkbox changes. Added togglePatchMode() to disable the
port side selector when is_patch_panel is checked, with an explanatory
note that all ports get doubled to front+back anyway. Also initializes
both states on page load so edit view reflects saved values.