feat: preserve portfolio triage arrival context (#218)
## Summary
- preserve portfolio triage arrival context from workspace overview and tenant registry drill-throughs
- add a tenant dashboard continuity widget plus bounded arrival token and resolver support
- add focused Pest coverage for arrival routing, return flow, RBAC degradation, and request-local performance
- include the Spec 187 spec, plan, research, data model, quickstart, contract, and tasks artifacts
## Validation
- integrated browser smoke: workspace overview -> tenant dashboard arrival -> backup sets CTA
- integrated browser smoke: tenant registry triage -> tenant dashboard arrival -> return to tenant triage
- branch includes focused automated test coverage for the new arrival-context surfaces
Co-authored-by: Ahmed Darrazi <ahmed.darrazi@live.de>
Reviewed-on: #218
ahmido
28e62bd22c