fix(anthropic): 补齐创建账号页自动透传开关并验证后端透传参数

- 在 CreateAccountModal 为 Anthropic API Key 增加自动透传开关

- 创建请求写入 extra.anthropic_passthrough 并补充状态重置

- 新增 AccountHandler 单测，验证 extra 字段从请求到 CreateAccountInput 的透传

backend/internal/handler/admin/account_handler_passthrough_test.go

@@ -0,0 +1,67 @@
+package admin
+
+import (
+	"bytes"
+	"encoding/json"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"github.com/gin-gonic/gin"
+	"github.com/stretchr/testify/require"
+)
+
+func TestAccountHandler_Create_AnthropicAPIKeyPassthroughExtraForwarded(t *testing.T) {
+	gin.SetMode(gin.TestMode)
+
+	adminSvc := newStubAdminService()
+	handler := NewAccountHandler(
+		adminSvc,
+		nil,
+		nil,
+		nil,
+		nil,
+		nil,
+		nil,
+		nil,
+		nil,
+		nil,
+		nil,
+		nil,
+	)
+
+	router := gin.New()
+	router.POST("/api/v1/admin/accounts", handler.Create)
+
+	body := map[string]any{
+		"name":     "anthropic-key-1",
+		"platform": "anthropic",
+		"type":     "apikey",
+		"credentials": map[string]any{
+			"api_key":  "sk-ant-xxx",
+			"base_url": "https://api.anthropic.com",
+		},
+		"extra": map[string]any{
+			"anthropic_passthrough": true,
+		},
+		"concurrency": 1,
+		"priority":    1,
+	}
+	raw, err := json.Marshal(body)
+	require.NoError(t, err)
+
+	rec := httptest.NewRecorder()
+	req := httptest.NewRequest(http.MethodPost, "/api/v1/admin/accounts", bytes.NewReader(raw))
+	req.Header.Set("Content-Type", "application/json")
+	router.ServeHTTP(rec, req)
+
+	require.Equal(t, http.StatusOK, rec.Code)
+	require.Len(t, adminSvc.createdAccounts, 1)
+
+	created := adminSvc.createdAccounts[0]
+	require.Equal(t, "anthropic", created.Platform)
+	require.Equal(t, "apikey", created.Type)
+	require.NotNil(t, created.Extra)
+	require.Equal(t, true, created.Extra["anthropic_passthrough"])
+}
+