fix: deliver validated AI insight responses

internal/analytics/periods.go

@@ -119,6 +119,16 @@ func nextJalaliMonth(jy, jm int) (int, int) {
 	return jy, jm
 }
 
+// JalaliMonthBounds returns the Tehran-local start and inclusive end of the
+// Jalali month containing at. It is shared by deterministic business rules.
+func JalaliMonthBounds(at time.Time, location *time.Location) (time.Time, time.Time) {
+	local := at.In(location)
+	year, month, _ := gregorianToJalali(local.Year(), int(local.Month()), local.Day())
+	start := jalaliDate(year, month, 1, location)
+	nextYear, nextMonth := nextJalaliMonth(year, month)
+	return start, jalaliDate(nextYear, nextMonth, 1, location).AddDate(0, 0, -1)
+}
+
 func completePeriods(datasetStart, datasetMax time.Time, location *time.Location) []Period {
 	if datasetMax.Before(datasetStart) {
 		return nil