fix: validate empty intervals + antigravity platform pricing match

- Backend: reject intervals with all-null price fields on save
- Backend: filterValidIntervals skips empty intervals in pricing resolver
- Frontend: red border + asterisk on empty interval rows
- Backend: antigravity groups now match anthropic/gemini channel pricing

backend/internal/handler/admin/channel_handler.go

@@ -2,6 +2,7 @@ package admin
 
 import (
 	"errors"
+	"fmt"
 	"strconv"
 	"strings"
 
@@ -233,10 +234,26 @@ func validatePricingBillingMode(pricing []service.ChannelModelPricing) error {
 				return errors.New("per-request price or intervals required for per_request/image billing mode")
 			}
 		}
+		// 校验 interval：至少有一个价格字段非空
+		for _, iv := range p.Intervals {
+			if iv.InputPrice == nil && iv.OutputPrice == nil &&
+				iv.CacheWritePrice == nil && iv.CacheReadPrice == nil &&
+				iv.PerRequestPrice == nil {
+				return fmt.Errorf("interval [%d, %s] has no price fields set for model %v",
+					iv.MinTokens, formatMaxTokens(iv.MaxTokens), p.Models)
+			}
+		}
 	}
 	return nil
 }
 
+func formatMaxTokens(max *int) string {
+	if max == nil {
+		return "∞"
+	}
+	return fmt.Sprintf("%d", *max)
+}
+
 // --- Handlers ---
 
 // List handles listing channels with pagination

backend/internal/service/model_pricing_resolver.go

@@ -106,9 +106,12 @@ func (r *ModelPricingResolver) applyChannelOverrides(ctx context.Context, groupI
 
 // applyTokenOverrides 应用 token 模式的渠道覆盖
 func (r *ModelPricingResolver) applyTokenOverrides(chPricing *ChannelModelPricing, resolved *ResolvedPricing) {
-	// 如果有区间定价，使用区间
-	if len(chPricing.Intervals) > 0 {
-		resolved.Intervals = chPricing.Intervals
+	// 过滤掉所有价格字段都为空的无效 interval
+	validIntervals := filterValidIntervals(chPricing.Intervals)
+
+	// 如果有有效的区间定价，使用区间
+	if len(validIntervals) > 0 {
+		resolved.Intervals = validIntervals
 		return
 	}
 
@@ -147,6 +150,20 @@ func (r *ModelPricingResolver) applyRequestTierOverrides(chPricing *ChannelModel
 	}
 }
 
+// filterValidIntervals 过滤掉所有价格字段都为空的无效 interval。
+// 前端可能创建了只有 min/max 但无价格的空 interval。
+func filterValidIntervals(intervals []PricingInterval) []PricingInterval {
+	var valid []PricingInterval
+	for _, iv := range intervals {
+		if iv.InputPrice != nil || iv.OutputPrice != nil ||
+			iv.CacheWritePrice != nil || iv.CacheReadPrice != nil ||
+			iv.PerRequestPrice != nil {
+			valid = append(valid, iv)
+		}
+	}
+	return valid
+}
+
 // GetIntervalPricing 根据 context token 数获取区间定价。
 // 如果有区间列表，找到匹配区间并构造 ModelPricing；否则直接返回 BasePricing。
 func (r *ModelPricingResolver) GetIntervalPricing(resolved *ResolvedPricing, totalContextTokens int) *ModelPricing {