Add TFR warning banner for airspace restrictions

Fetches active Temporary Flight Restrictions from the FAA website,
filters by configured state (LOCATION_STATE env var), and displays
a red warning banner at the top of the dashboard when TFRs are present.
Data is cached for 30 minutes and degrades gracefully if the FAA is unreachable.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/internal/server/routes.go

@@ -14,6 +14,7 @@ type RouteHandler interface {
 	GetForecast(w http.ResponseWriter, r *http.Request)
 	GetHistorical(w http.ResponseWriter, r *http.Request)
 	AssessConditions(w http.ResponseWriter, r *http.Request)
+	GetTFRs(w http.ResponseWriter, r *http.Request)
 }
 
 // SetupRoutes configures all API routes
@@ -30,6 +31,11 @@ func (s *Server) SetupRoutes(handler RouteHandler) {
 			r.Get("/historical", handler.GetHistorical)
 			r.Post("/assess", handler.AssessConditions)
 		})
+
+		// Airspace routes
+		r.Route("/airspace", func(r chi.Router) {
+			r.Get("/tfrs", handler.GetTFRs)
+		})
 	})
 }