New /organizations route under Tenancy. Lists every org in the current
tenant (via GET /api/v1/admin/organizations), with per-row Manage
members and Settings dialogs.
- Members dialog: invite by email, add restricted sub-user, change role,
transfer ownership, remove member (owner removal honors the org's
on_owner_removal policy server-side)
- Settings dialog: edit name, status (active/frozen/pending_deletion),
and on_owner_removal policy
- app/lib/arcadia/organizations.ts: typed client for the new endpoints
- Nav entry added under Tenancy group
Tenant admins bypass per-org membership checks via the backend's
OrganizationContext plug, so the per-org REST endpoints work for any
org in the tenant without an explicit /admin/* surface.
a299900021