fix(map): revert to Leaflet + proxied OSM tiles, add CPE signal to popups

Reverted from MapLibre/PMTiles to Leaflet with nginx-proxied OSM raster
tiles — the MapLibre approach had unresolvable CSP and theme compat
issues. The proxy keeps all browser requests local (no third-party).

Also:
- Add CPE signal strength and parent AP name to fleet summary SQL
  and map popup cards (e.g. "Signal: -62 dBm to ap-shady-north")
- Add .dockerignore to exclude 8GB PMTiles and node_modules from
  Docker build context (was causing 10+ minute builds)
- Configure mailpit SMTP in dev compose

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

frontend/package.json

@@ -20,7 +20,6 @@
     "@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",
@@ -51,8 +50,6 @@
     "framer-motion": "^12.34.3",
     "leaflet": "^1.9.4",
     "lucide-react": "^0.575.0",
-    "maplibre-gl": "^5.20.2",
-    "pmtiles": "^4.4.0",
     "react": "^19.2.0",
     "react-dom": "^19.2.0",
     "react-leaflet": "^5.0.0",