feat(ops): 运维监控新增 OpenAI Token 请求统计表

- 新增管理端接口 /api/v1/admin/ops/dashboard/openai-token-stats，按模型聚合统计 gpt% 请求

- 支持 time_range=30m|1h|1d|15d|30d（默认 30d），支持 platform/group_id 过滤

- 支持分页（page/page_size）或 TopN（top_n）互斥查询

- 前端运维监控页新增统计表卡片，包含空态/错误态与分页/TopN 交互

- 补齐后端与前端测试

backend/internal/handler/admin/admin_helpers_test.go

@@ -58,6 +58,96 @@ func TestParseOpsDuration(t *testing.T) {
 	require.False(t, ok)
 }
 
+func TestParseOpsOpenAITokenStatsDuration(t *testing.T) {
+	tests := []struct {
+		input string
+		want  time.Duration
+		ok    bool
+	}{
+		{input: "30m", want: 30 * time.Minute, ok: true},
+		{input: "1h", want: time.Hour, ok: true},
+		{input: "1d", want: 24 * time.Hour, ok: true},
+		{input: "15d", want: 15 * 24 * time.Hour, ok: true},
+		{input: "30d", want: 30 * 24 * time.Hour, ok: true},
+		{input: "7d", want: 0, ok: false},
+	}
+
+	for _, tt := range tests {
+		got, ok := parseOpsOpenAITokenStatsDuration(tt.input)
+		require.Equal(t, tt.ok, ok, "input=%s", tt.input)
+		require.Equal(t, tt.want, got, "input=%s", tt.input)
+	}
+}
+
+func TestParseOpsOpenAITokenStatsFilter_Defaults(t *testing.T) {
+	gin.SetMode(gin.TestMode)
+	w := httptest.NewRecorder()
+	c, _ := gin.CreateTestContext(w)
+	c.Request = httptest.NewRequest(http.MethodGet, "/", nil)
+
+	before := time.Now().UTC()
+	filter, err := parseOpsOpenAITokenStatsFilter(c)
+	after := time.Now().UTC()
+
+	require.NoError(t, err)
+	require.NotNil(t, filter)
+	require.Equal(t, "30d", filter.TimeRange)
+	require.Equal(t, 1, filter.Page)
+	require.Equal(t, 20, filter.PageSize)
+	require.Equal(t, 0, filter.TopN)
+	require.Nil(t, filter.GroupID)
+	require.Equal(t, "", filter.Platform)
+	require.True(t, filter.StartTime.Before(filter.EndTime))
+	require.WithinDuration(t, before.Add(-30*24*time.Hour), filter.StartTime, 2*time.Second)
+	require.WithinDuration(t, after, filter.EndTime, 2*time.Second)
+}
+
+func TestParseOpsOpenAITokenStatsFilter_WithTopN(t *testing.T) {
+	gin.SetMode(gin.TestMode)
+	w := httptest.NewRecorder()
+	c, _ := gin.CreateTestContext(w)
+	c.Request = httptest.NewRequest(
+		http.MethodGet,
+		"/?time_range=1h&platform=openai&group_id=12&top_n=50",
+		nil,
+	)
+
+	filter, err := parseOpsOpenAITokenStatsFilter(c)
+	require.NoError(t, err)
+	require.Equal(t, "1h", filter.TimeRange)
+	require.Equal(t, "openai", filter.Platform)
+	require.NotNil(t, filter.GroupID)
+	require.Equal(t, int64(12), *filter.GroupID)
+	require.Equal(t, 50, filter.TopN)
+	require.Equal(t, 0, filter.Page)
+	require.Equal(t, 0, filter.PageSize)
+}
+
+func TestParseOpsOpenAITokenStatsFilter_InvalidParams(t *testing.T) {
+	tests := []string{
+		"/?time_range=7d",
+		"/?group_id=0",
+		"/?group_id=abc",
+		"/?top_n=0",
+		"/?top_n=101",
+		"/?top_n=10&page=1",
+		"/?top_n=10&page_size=20",
+		"/?page=0",
+		"/?page_size=0",
+		"/?page_size=101",
+	}
+
+	gin.SetMode(gin.TestMode)
+	for _, rawURL := range tests {
+		w := httptest.NewRecorder()
+		c, _ := gin.CreateTestContext(w)
+		c.Request = httptest.NewRequest(http.MethodGet, rawURL, nil)
+
+		_, err := parseOpsOpenAITokenStatsFilter(c)
+		require.Error(t, err, "url=%s", rawURL)
+	}
+}
+
 func TestParseOpsTimeRange(t *testing.T) {
 	gin.SetMode(gin.TestMode)
 	w := httptest.NewRecorder()