chore: add model gpt-5.5

backend/internal/service/billing_service.go

@@ -217,6 +217,9 @@ func (s *BillingService) initFallbackPricing() {
 		LongContextInputMultiplier:     openAIGPT54LongContextInputMultiplier,
 		LongContextOutputMultiplier:    openAIGPT54LongContextOutputMultiplier,
 	}
+	// GPT-5.5 暂无独立定价，回退到 GPT-5.4
+	s.fallbackPrices["gpt-5.5"] = s.fallbackPrices["gpt-5.4"]
+
 	s.fallbackPrices["gpt-5.4-mini"] = &ModelPricing{
 		InputPricePerToken:     7.5e-7,
 		OutputPricePerToken:    4.5e-6,
@@ -288,6 +291,8 @@ func (s *BillingService) getFallbackPricing(model string) *ModelPricing {
 	if strings.Contains(modelLower, "gpt-5") || strings.Contains(modelLower, "codex") {
 		normalized := normalizeCodexModel(modelLower)
 		switch normalized {
+		case "gpt-5.5":
+			return s.fallbackPrices["gpt-5.5"]
 		case "gpt-5.4-mini":
 			return s.fallbackPrices["gpt-5.4-mini"]
 		case "gpt-5.4":
@@ -637,7 +642,8 @@ func isOpenAIGPT54Model(model string) bool {
 	if !strings.Contains(trimmed, "gpt-5") && !strings.Contains(trimmed, "codex") {
 		return false
 	}
-	return normalizeCodexModel(trimmed) == "gpt-5.4"
+	normalized := normalizeCodexModel(trimmed)
+	return normalized == "gpt-5.4" || normalized == "gpt-5.5"
 }
 
 // CalculateCostWithConfig 使用配置中的默认倍率计算费用