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/components/map/MapPage.tsx

@@ -73,7 +73,7 @@ export function MapPage() {
   }
 
   return (
-    <div className="flex flex-col h-full">
+    <div className="flex flex-col" style={{ height: 'calc(100vh - 6rem)' }}>
       {/* Toolbar */}
       <div className="flex items-center justify-between px-4 py-2 border-b border-border bg-sidebar shrink-0">
         <div className="flex items-center gap-3">