[WIP] Add MET Norway as a weather API provider

[Copilot]

• Add 'met.no': 'MET Norway' to WEATHER_PROVIDERS constant
• Add Nominatim geocoding function (free, no API key needed) with caching for lat/lon lookup
• Add MET Norway API fetch function using locationforecast/2.0/complete endpoint
• Add weather data parser (parseMetNoWeatherData) for current conditions
• Add forecast data parser (parseMetNoForecastData) for multi-day forecasts
• Add symbol_code to human-readable description mapping
• Add met.no case to getWeatherByProvider() switch statement
• Add met.no case to getForecastByProvider() switch statement
• Add MET Norway option to provider dropdown in settings HTML (🆓 free)

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