feat: implement external API integration with static tide tables (task 32)

- Add in-memory caching for external API responses (6-hour expiration)
- Implement OpenWeatherMap integration for weather data
- Create static tide tables for 22 Irish coastal stations
- Add tide calculation based on semi-diurnal patterns and lunar cycles
- Implement water quality, beach quality, and biodiversity placeholder endpoints
- Add comprehensive API documentation (EXTERNAL_API_SETUP.md)
- Fix frontend WaterQualityIndicator crash
- Remove Redis dependency (using in-memory cache instead)
- All external data endpoints functional and tested

src/components/external/WaterQualityIndicator.tsx

@@ -62,7 +62,7 @@ export function WaterQualityIndicator({ latitude, longitude }: WaterQualityIndic
     );
   }
 
-  const statusConfig = {
+  const statusConfig: Record<string, { color: string; text: string; icon: string }> = {
     excellent: { color: 'bg-green-500', text: 'Excellent', icon: '✓' },
     good: { color: 'bg-blue-500', text: 'Good', icon: '✓' },
     sufficient: { color: 'bg-yellow-500', text: 'Sufficient', icon: '!' },
@@ -70,7 +70,7 @@ export function WaterQualityIndicator({ latitude, longitude }: WaterQualityIndic
     unknown: { color: 'bg-gray-400', text: 'Unknown', icon: '?' },
   };
 
-  const config = statusConfig[waterQuality.status];
+  const config = statusConfig[waterQuality.status] || statusConfig.unknown;
 
   return (
     <div className="bg-white rounded-lg shadow p-4">