Show current weather on the Overview

Add a weather card to the Web App Overview, wired like the OpenSky live-map
overlay and backed by the OpenWeather plugin.

- API Server: GET /api/integrations/openweather/current resolves the
  caller's cascade, gates it (master/org/personal opt-in/key), and returns
  trimmed current conditions for the configured or a supplied ?lat=&lon=
  point; off/keyless returns {unavailable, detail} so the card degrades.
- BFF relay (forwards the location override) + route; api.js client.
- Dashboard: a Weather card stacked above Schedule showing an emoji
  condition, temperature in the resolved unit, description, location, and a
  feels-like/wind/humidity/cloud grid. Location follows the same cascade as
  the map (drone -> phone -> browser -> default) without prompting for geo;
  refreshes every 10 min while on Overview.
- validLatLon test; rebuilt embedded frontend.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

API Server/internal/api/server.go

@@ -115,6 +115,7 @@ func (s *Server) Handler() http.Handler {
 	mux.HandleFunc("GET /api/integrations/openweather", s.handleGetOpenWeather)
 	mux.HandleFunc("PUT /api/integrations/openweather", s.handlePutOpenWeather)
 	mux.HandleFunc("POST /api/integrations/openweather/health", s.handleOpenWeatherHealth)
+	mux.HandleFunc("GET /api/integrations/openweather/current", s.handleOpenWeatherCurrent)
 
 	// User-management — gated on the caller being a manager (admin or superadmin).
 	// Admins are scoped to their own organization inside each handler.