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>

.dockerignore

@@ -0,0 +1,10 @@
+frontend/public/tiles/
+frontend/node_modules/
+docker-data/
+.worktrees/
+.git/
+.planning/
+.superpowers/
+docs/superpowers/
+tools/dev/
+*.pmtiles