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>

docker-compose.override.yml

@@ -27,6 +27,9 @@ services:
       JWT_SECRET_KEY: ${JWT_SECRET_KEY:?Set JWT_SECRET_KEY in .env}
       OPENBAO_ADDR: http://openbao:8200
       OPENBAO_TOKEN: dev-openbao-token
+      SMTP_HOST: mailpit
+      SMTP_PORT: "1025"
+      SMTP_USE_TLS: "false"
       GIT_STORE_PATH: /data/git-store
       WIREGUARD_CONFIG_PATH: /data/wireguard
       WIREGUARD_GATEWAY: wireguard