Add sunset time display to weather forecast UI

[Copilot]

Integrates the new backend /sunset and /sunset/range endpoints into the weather forecast table.

Changes

• SunsetInfo.cs: Model matching backend response schema
• SunsetClient.cs: HTTP client wrapping sunset endpoints
• Program.cs: Registers SunsetClient in DI container
• FetchData.razor: Adds "Sunset Time" column with Dictionary-based lookup for O(1) access

// Efficient lookup instead of linear search per row
var sunsetTimes = await SunsetClient.GetSunsetRangeAsync(startDate, 5);
sunsetLookup = sunsetTimes.ToDictionary(s => s.Date);

// In render loop
sunsetLookup.TryGetValue(forecast.Date, out var sunset);
<td>@(sunset?.FormattedTime ?? "N/A")</td>

Screenshot

Original prompt

Update the UI to support the newly added controller endpoint of returnning the sunset time of a day

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