feat(reports): align first response distribution range

internal/handler/api/v1/analytics_handler.go

@@ -566,7 +566,7 @@ func (h *AnalyticsHandler) FirstResponseTimeDistribution(c *gin.Context) {
 	if !ok {
 		return
 	}
-	since, until, ok := parseDateRange(c)
+	since, until, ok := parseOptionalReportDateRange(c)
 	if !ok {
 		return
 	}
@@ -581,6 +581,25 @@ func (h *AnalyticsHandler) FirstResponseTimeDistribution(c *gin.Context) {
 	c.JSON(http.StatusOK, result)
 }
 
+func parseOptionalReportDateRange(c *gin.Context) (since, until time.Time, ok bool) {
+	sinceRaw := c.Query("since")
+	untilRaw := c.Query("until")
+	if sinceRaw == "" || untilRaw == "" {
+		return time.Time{}, time.Time{}, true
+	}
+	since, err := parseChatwootReportTime(sinceRaw)
+	if err != nil {
+		response.AbortWithStatusError(c, http.StatusBadRequest, response.ErrBadRequest, "invalid since date format")
+		return time.Time{}, time.Time{}, false
+	}
+	until, err = parseChatwootReportTime(untilRaw)
+	if err != nil {
+		response.AbortWithStatusError(c, http.StatusBadRequest, response.ErrBadRequest, "invalid until date format")
+		return time.Time{}, time.Time{}, false
+	}
+	return since, until, true
+}
+
 // OutgoingMessagesCount returns outgoing message count metrics.
 // GET /api/v1/accounts/:account_id/reports/outgoing_messages_count
 // Reference: Chatwoot reports#outgoing_messages_count