feat: implement Forecast 2026 (Fc 26) tab with seasonality logic and actual sales comparison

types.ts

@@ -194,3 +194,22 @@ export interface CombinedKPIs {
   cvrUnits: number;
   glanceViews: number;   // Traffic / page views
 }
+
+export interface ForecastRecord {
+  asin: string;
+  annualForecast: number;
+}
+
+export interface MonthlyForecastPoint {
+  month: string;
+  forecastUnits: number;
+  actualUnits: number;
+}
+
+export interface ProductForecastData {
+  asin: string;
+  sku: string;
+  title: string;
+  annualForecast: number;
+  monthlyData: MonthlyForecastPoint[];
+}