[AZ-1126] Migrate capturedAt to DateTimeOffset

Co-authored-by: Cursor <cursoragent@cursor.com>

SatelliteProvider.Common/Json/UtcOffsetRequiredDateTimeOffsetConverter.cs

@@ -0,0 +1,43 @@
+using System.Globalization;
+using System.Text.Json;
+using System.Text.Json.Serialization;
+using System.Text.RegularExpressions;
+
+namespace SatelliteProvider.Common.Json;
+
+public sealed partial class UtcOffsetRequiredDateTimeOffsetConverter : JsonConverter<DateTimeOffset>
+{
+    [GeneratedRegex(@"T\d{2}:\d{2}(:\d{2}(\.\d+)?)?(Z|[+-]\d{2}:\d{2}|[+-]\d{4})$", RegexOptions.IgnoreCase | RegexOptions.CultureInvariant)]
+    private static partial Regex ExplicitOffsetPattern();
+
+    public override DateTimeOffset Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
+    {
+        if (reader.TokenType != JsonTokenType.String)
+        {
+            throw new JsonException("`capturedAt` must be an ISO-8601 string with an explicit UTC offset.");
+        }
+
+        var raw = reader.GetString();
+        if (string.IsNullOrWhiteSpace(raw))
+        {
+            throw new JsonException("`capturedAt` must be an ISO-8601 string with an explicit UTC offset.");
+        }
+
+        if (!ExplicitOffsetPattern().IsMatch(raw))
+        {
+            throw new JsonException("`capturedAt` must include an explicit UTC offset (for example `Z` or `+00:00`).");
+        }
+
+        if (!DateTimeOffset.TryParse(raw, CultureInfo.InvariantCulture, DateTimeStyles.RoundtripKind, out var parsed))
+        {
+            throw new JsonException("`capturedAt` could not be parsed as an ISO-8601 timestamp.");
+        }
+
+        return parsed.ToUniversalTime();
+    }
+
+    public override void Write(Utf8JsonWriter writer, DateTimeOffset value, JsonSerializerOptions options)
+    {
+        writer.WriteStringValue(value.ToUniversalTime().ToString("O", CultureInfo.InvariantCulture));
+    }
+}