Ralph Context

Follow the approved design in docs/superpowers/specs/2026-03-13-gitea-agentic-runtime-design.md.
Execute tasks from docs/superpowers/plans/2026-03-13-gitea-agentic-runtime-plan.md in order.
Keep Gitea as the only real provider in this iteration.
Preserve platform-agnostic boundaries so GitHub can be added later.