Comprehensive documentation for the new customer pre-order workflow:
- Added docs/PREORDER/README.md with process, entities, lifecycle, and workflow details
- Registered topic code PREO in docs/TOPIC_CODES.md
- Added PREORDER_ISSUES.md and PREORDER_TODO.md for tracking
- Updated README.md, DOMAIN_MODEL.md, MEASUREMENT.md, and topic folder lists to reference pre-orders
- Enhanced SCHEMA.md with pre-order entity clarifications and business logic
- Integrated pre-orders as a fourth main domain workflow
Comprehensively renamed all "Preorder" domain types, services, controllers, models, enums, database contexts, routes, views, JS, localization resources, and documentation to "PreOrder" (PascalCase, capital "O"). Updated all references in backend, frontend, localization, and schema docs for consistency. No business logic changes; this is a naming and normalization refactor.