fix: route workspace switch to chooser (#147)
## Summary
- route the context-bar `Switch workspace` link to the canonical chooser flow instead of workspace management
- add focused regression coverage for topbar switching, management separation, and chooser redirect semantics
- add Spec 121 artifacts (`spec`, `plan`, `research`, `data-model`, `contracts`, `quickstart`, `tasks`, checklist)
## Validation
- `vendor/bin/sail artisan test --compact tests/Feature/Monitoring/HeaderContextBarTest.php tests/Feature/Workspaces/WorkspaceSwitchUserMenuTest.php tests/Feature/Workspaces/ChooseWorkspacePageTest.php tests/Feature/Workspaces/WorkspaceNavigationHubTest.php tests/Feature/Workspaces/EnsureWorkspaceSelectedMiddlewareTest.php tests/Feature/Workspaces/ChooseWorkspaceRedirectsToChooseTenantTest.php`
- `vendor/bin/sail bin pint --dirty --format agent`
## Notes
- base branch: `dev`
- branch: `121-workspace-switch-fix`
Co-authored-by: Ahmed Darrazi <ahmed.darrazi@live.de>
Reviewed-on: #147
ahmido
891f177311