feat(backend): 添加 Gemini V1beta Handler 和路由

- 新增 gemini_v1beta_handler.go: 代理原生 Google API 格式
- 更新 gemini_oauth_handler.go: 移除 redirectUri，新增 oauthType
- 更新 account_handler.go: 账户 Handler 增强
- 更新 router.go: 注册 v1beta 路由
- 更新 config.go: Gemini OAuth 通过环境变量配置
- 更新 wire_gen.go: 依赖注入

backend/internal/server/router.go

@@ -314,6 +314,16 @@ func registerRoutes(r *gin.Engine, h *handler.Handlers, s *service.Services, rep
 		gateway.POST("/responses", h.OpenAIGateway.Responses)
 	}
 
+	// Gemini 原生 API 兼容层（Gemini SDK/CLI 直连）
+	gemini := r.Group("/v1beta")
+	gemini.Use(middleware.ApiKeyAuthWithSubscriptionGoogle(s.ApiKey, s.Subscription))
+	{
+		gemini.GET("/models", h.Gateway.GeminiV1BetaListModels)
+		gemini.GET("/models/:model", h.Gateway.GeminiV1BetaGetModel)
+		// Gin treats ":" as a param marker, but Gemini uses "{model}:{action}" in the same segment.
+		gemini.POST("/models/*modelAction", h.Gateway.GeminiV1BetaModels)
+	}
+
 	// OpenAI Responses API（不带v1前缀的别名）
 	r.POST("/responses", middleware.ApiKeyAuthWithSubscription(s.ApiKey, s.Subscription), h.OpenAIGateway.Responses)
 }