Dos primitivas reutilizables para apps web del registry:
- random_hex_id_go_core: IDs hex aleatorios (apps con SQLite + IDs string)
- spa_handler_go_infra: http.Handler que sirve embed.FS con fallback
a index.html (patron SPA para React Router/dnd-kit)
Ambas creadas via fn-constructor durante apps/kanban (issue 0053).
Tests pasan, fn index OK.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
