feat(14-03): add site dashboard components (health grid, sector view, links tab)

- SiteHealthGrid shows device cards with status dots, CPU/memory bars, uptime
- SectorFormDialog supports create and edit modes for sectors
- SiteSectorView groups APs by sector with collapsible sections, connected CPE lists, aggregate stats, sector assignment dropdown
- SiteLinksTab wraps WirelessLinksTable with siteId filtering
- Add sector_id and sector_name to DeviceResponse, site_id/sector_id to DeviceListParams

frontend/src/lib/api.ts

@@ -308,6 +308,8 @@ export interface DeviceResponse {
   groups: DeviceGroupRef[]
   site_id: string | null
   site_name: string | null
+  sector_id: string | null
+  sector_name: string | null
   created_at: string
 }
 
@@ -348,6 +350,8 @@ export interface DeviceListParams {
   status?: string
   model?: string
   tag?: string
+  site_id?: string
+  sector_id?: string
 }
 
 export const devicesApi = {