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/package.json

@@ -20,6 +20,7 @@
     "@fontsource/ibm-plex-mono": "^5.2.7",
     "@git-diff-view/lowlight": "^0.0.39",
     "@git-diff-view/react": "^0.0.39",
+    "@protomaps/basemaps": "^5.7.2",
     "@radix-ui/react-avatar": "^1.1.11",
     "@radix-ui/react-checkbox": "^1.3.3",
     "@radix-ui/react-dialog": "^1.1.15",
@@ -50,7 +51,8 @@
     "framer-motion": "^12.34.3",
     "leaflet": "^1.9.4",
     "lucide-react": "^0.575.0",
-    "protomaps-leaflet": "^5.1.0",
+    "maplibre-gl": "^5.20.2",
+    "pmtiles": "^4.4.0",
     "react": "^19.2.0",
     "react-dom": "^19.2.0",
     "react-leaflet": "^5.0.0",