feat(gateway): 对所有请求（包括 Codex CLI）应用模型映射

- 移除 Codex CLI 的模型映射跳过逻辑
- 添加详细的模型映射日志，包含账号名称和请求类型
- 确保所有 OpenAI 请求都能正确应用账号配置的模型映射

backend/internal/service/openai_gateway_service.go

@@ -545,14 +545,12 @@ func (s *OpenAIGatewayService) Forward(ctx context.Context, c *gin.Context, acco
 
 	isCodexCLI := openai.IsCodexCLIRequest(c.GetHeader("User-Agent"))
 
-	// Apply model mapping (skip for Codex CLI for transparent forwarding)
-	mappedModel := reqModel
-	if !isCodexCLI {
-		mappedModel = account.GetMappedModel(reqModel)
-		if mappedModel != reqModel {
-			reqBody["model"] = mappedModel
-			bodyModified = true
-		}
+	// Apply model mapping for all requests (including Codex CLI)
+	mappedModel := account.GetMappedModel(reqModel)
+	if mappedModel != reqModel {
+		log.Printf("[OpenAI] Model mapping applied: %s -> %s (account: %s, isCodexCLI: %v)", reqModel, mappedModel, account.Name, isCodexCLI)
+		reqBody["model"] = mappedModel
+		bodyModified = true
 	}
 
 	if account.Type == AccountTypeOAuth && !isCodexCLI {