feat: add salary insights

Models/AnalyticsDtos.cs

@@ -21,6 +21,8 @@ namespace JobTrackerApi.Models
 
     public sealed record StageDurationDto(string Stage, double MedianDays, int Count);
 
+    public sealed record SalaryInsightDto(string Currency, string Period, int Count, decimal Minimum, decimal Maximum, decimal AverageMidpoint);
+
     public sealed record AnalyticsOverviewDto(
         List<FunnelStagePoint> Funnel,
         List<ResponseRatePoint> ResponseRateBySource,
@@ -28,6 +30,7 @@ namespace JobTrackerApi.Models
         double? MedianDaysToFirstResponse,
         int TotalResponses,
         int TotalActive,
-        List<StageDurationDto> TimeInStage
+        List<StageDurationDto> TimeInStage,
+        List<SalaryInsightDto> SalaryInsights
     );
 }