Add CapacityInsightWorker (every 15 min) that generates critical/warning
insights when backhaul utilization exceeds 90%/75% and auto-resolves
when it drops below 70%.
Add capacity and utilization columns to the device ports tab with
set/clear capacity controls. Add organization-level /capacity page
with summary cards and per-site capacity table. Add capacity summary
card to site show page. Add Capacity link to nav menu.
