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>

frontend/lib/api.ts

@@ -3,6 +3,7 @@ import {
   ForecastResponse,
   HistoricalResponse,
   AssessmentResponse,
+  TFRResponse,
   Thresholds,
   APIError,
 } from './types'
@@ -166,6 +167,13 @@ class APIClient {
     }
   }
 
+  /**
+   * Get active TFRs (Temporary Flight Restrictions) near the configured location
+   */
+  async getTfrs(): Promise<TFRResponse> {
+    return this.request<TFRResponse>('/airspace/tfrs')
+  }
+
   /**
    * Assess current conditions with custom thresholds
    */
@@ -200,6 +208,8 @@ export const getForecast = (lat?: number, lon?: number) =>
 export const getHistorical = (date: string, lat?: number, lon?: number) =>
   apiClient.getHistorical(date, lat, lon)
 
+export const getTfrs = () => apiClient.getTfrs()
+
 export const assessWithThresholds = (
   thresholds: Thresholds,
   lat?: number,