feat(map): self-hosted MapLibre GL + PMTiles vector map

Replace Leaflet + OSM raster tiles with MapLibre GL JS + PMTiles:
- Full continental US vector tiles (8GB PMTiles, zoom 0-14 with overzoom)
- Dark theme via @protomaps/basemaps (official supported path)
- Clustered device markers with status colors (green/yellow/red)
- Popup cards show CPU, memory, wireless client count + avg signal
- Font glyphs proxied through nginx, sprites served locally
- Zero third-party requests from the browser
- Fleet summary SQL now includes wireless client count and avg signal
  via LEFT JOIN LATERAL on wireless_links

Also removes alert toast spam and fixes map container height.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/lib/api.ts

@@ -807,6 +807,8 @@ export interface FleetDevice {
   longitude: number | null
   tenant_id: string
   tenant_name: string
+  client_count: number | null
+  avg_signal: number | null
 }
 
 export interface SparklinePoint {