test: add repository and domain tests

- Add pagination result tests (internal/repository/pagination.go)
- Add Gemini drive client factory test (internal/repository/gemini_drive_client.go)
- Add scanSingleRow contract tests (internal/repository/sql_scan.go)
- Add DefaultThemeConfig test (internal/domain/theme.go)

Coverage improvements:
- repository: 75.8%
- domain: 21.1%

internal/repository/gemini_drive_client_test.go

@@ -0,0 +1,15 @@
+package repository
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestNewGeminiDriveClient(t *testing.T) {
+	client := NewGeminiDriveClient()
+	require.NotNil(t, client)
+	
+	// 返回的是接口类型，只要不为 nil 即可
+	// 具体功能在 geminicli 包中测试
+}