Coach can work in multiple companies with one account (multi-tenant) + fast company/location switcher

As a coach, I want to be able to be a member of multiple companies (multi-tenant) with a single email address/password and be able to switch between companies/locations within the coaching environment without logging out or logging back in. Think of a clear “Active company/location” switcher, remembering the last used company, and strict data separation per company (clients, calendar, products, settings, branding, billing/permissions).