docs: update all documentation for OpenCode and deployment

- Update architecture.md with spawn service and auth proxy sections
- Update deployment.md with production stack details
- Update development.md with spawn workflow documentation
- Update mvp-scope.md, project-brief.md, tool-manifest-spec.md
- Update conversation-handoff.md with current status
- Replace all RunFusion references with OpenCode

docs/conversation-handoff.md

@@ -62,7 +62,7 @@ This document captures the key architectural decisions, assumptions, and open lo
 - **FN-004:** Backend Foundation — depends on the PostgreSQL domain model in Section 4
 - **FN-005:** Frontend Foundation — depends on component boundaries in Section 3.1
 - **FN-006:** Deployment Config — depends on Traefik routing model in Section 10
-- **FN-008:** RunFusion POC — depends on spawn lifecycle in Section 8 and Docker runtime in Section 9
+- **FN-008:** OpenCode POC — depends on spawn lifecycle in Section 8 and Docker runtime in Section 9
 - **FN-009:** Config & Secrets — depends on storage layout in Section 11 and security in Section 13
 - **FN-010:** code-server Spawn — depends on tool manifest in Section 7 and Docker runtime in Section 9
 - **FN-011:** Git Provider — depends on Git provider abstraction in Section 5