docs: comprehensive documentation update
- DATABASE.md: Complete schema with ER diagram, all tables, migrations history
- ROADMAP.md: Project status, completed/in-progress/backlog items
- TASKS.md: Detailed task list to avoid rework
- README.md: Added documentation links table
- backoffice/README.md: Added auth section (JWT Bearer + Cookie)
Schema notes:
- Core tables use SERIAL (INT): users, companies, jobs
- Newer tables use UUID v4: notifications, tickets, payments
- Schema is unified (removed core_* redundant tables)
017a34c965