[codex] Unify module workbench routes

[ActiveInAI]

What changed

• Use UUID-safe default runtime context headers for frontend API calls so database-backed project routes no longer send dev-tenant.
• Route every business module, including Digital Twin, through /app/modules/{moduleId} and retire the standalone /app/digital-twin entry.
• Remove the unused standalone DigitalTwinWorkbench component and update architecture docs to match the unified Open CDE module workbench boundary.

Why

/app/projects was calling the database-backed backend with a non-UUID tenant id, which caused tenant_id must be a UUID. Digital Twin also had two competing surfaces, while the repository source of truth requires the module route to use the same Open CDE workbench as all other modules.

Validation

• bun x next typegen
• bun run typecheck
• bun run lint
• bun run test
• bun run build
• Restarted local database containers, backend gateway, and frontend dev server.
• Verified /v1/projects returns tenant-scoped projects with UUID headers.
• Verified /app/projects returns 200 and renders 2 projects.
• Verified all 14 module routes return 200 under /app/modules/....
• Verified /app/modules/digital_twin returns 200.
• Verified retired /app/digital-twin returns 404.