Neue Tenant-Tabellen work_order_milestones und billing_records (RLS, TENANT_MODELS, PII-Felder), Partial-Unique-Indizes je Quelle, billing_record_id an time_entries/material_usages. Rechte billing:read/billing:write (Backoffice, Mandantenadmin), Modul billing, Events milestone.*.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
