Provision a new tenant

Onboarding a real school on ClicknifyERP. This action creates the tenant row, derives an OKLCH brand ramp from the primary hex, seeds a landing page, unlocks the 5 core modules (attendance, fees, admissions, timetable, exams), provisions a default branch, and adds a Principal user record. Add-on modules are locked by default — the Principal can request unlock from their dashboard.