refactor(tests): enhance test infrastructure with library/collection helpers

- Add LibraryTestData struct to TestDeviceSetup
- Implement CreateLibrary() for proper library creation in tests
- Implement CreateCollection() for test collection support
- Improve test isolation with dedicated library creation

This provides a more robust foundation for integration tests that need
proper library management support.

cmd/server/tests/test_helpers_db.go

@@ -2,7 +2,6 @@ package main
 
 import (
 	"bookhoard/internal/database"
-	"bookhoard/internal/handlers"
 	"bytes"
 	"context"
 	"encoding/json"