fix(gemini): fetch model list via native v1beta/models endpoint

Use the native Gemini Models API (/v1beta/models) instead of the OpenAI-compatible
path when listing models for Gemini channels, improving compatibility with
third-party Gemini-format providers that don't implement OpenAI routes.

- Add paginated model listing with timeout and optional proxy support
- Select an enabled key for multi-key Gemini channels

controller/channel.go

@@ -11,6 +11,7 @@ import (
 	"github.com/QuantumNous/new-api/constant"
 	"github.com/QuantumNous/new-api/dto"
 	"github.com/QuantumNous/new-api/model"
+	"github.com/QuantumNous/new-api/relay/channel/gemini"
 	"github.com/QuantumNous/new-api/relay/channel/ollama"
 	"github.com/QuantumNous/new-api/service"
 
@@ -260,11 +261,37 @@ func FetchUpstreamModels(c *gin.Context) {
 		return
 	}
 
+	// 对于 Gemini 渠道，使用特殊处理
+	if channel.Type == constant.ChannelTypeGemini {
+		// 获取用于请求的可用密钥（多密钥渠道优先使用启用状态的密钥）
+		key, _, apiErr := channel.GetNextEnabledKey()
+		if apiErr != nil {
+			c.JSON(http.StatusOK, gin.H{
+				"success": false,
+				"message": fmt.Sprintf("获取渠道密钥失败: %s", apiErr.Error()),
+			})
+			return
+		}
+		key = strings.TrimSpace(key)
+		models, err := gemini.FetchGeminiModels(baseURL, key, channel.GetSetting().Proxy)
+		if err != nil {
+			c.JSON(http.StatusOK, gin.H{
+				"success": false,
+				"message": fmt.Sprintf("获取Gemini模型失败: %s", err.Error()),
+			})
+			return
+		}
+
+		c.JSON(http.StatusOK, gin.H{
+			"success": true,
+			"message": "",
+			"data":    models,
+		})
+		return
+	}
+
 	var url string
 	switch channel.Type {
-	case constant.ChannelTypeGemini:
-		// curl https://example.com/v1beta/models?key=$GEMINI_API_KEY
-		url = fmt.Sprintf("%s/v1beta/openai/models", baseURL) // Remove key in url since we need to use AuthHeader
 	case constant.ChannelTypeAli:
 		url = fmt.Sprintf("%s/compatible-mode/v1/models", baseURL)
 	case constant.ChannelTypeZhipu_v4:
@@ -1072,6 +1099,23 @@ func FetchModels(c *gin.Context) {
 		return
 	}
 
+	if req.Type == constant.ChannelTypeGemini {
+		models, err := gemini.FetchGeminiModels(baseURL, key, "")
+		if err != nil {
+			c.JSON(http.StatusOK, gin.H{
+				"success": false,
+				"message": fmt.Sprintf("获取Gemini模型失败: %s", err.Error()),
+			})
+			return
+		}
+
+		c.JSON(http.StatusOK, gin.H{
+			"success": true,
+			"data":    models,
+		})
+		return
+	}
+
 	client := &http.Client{}
 	url := fmt.Sprintf("%s/v1/models", baseURL)