refactor(routing): externalize API path configuration for API gateway compatibility

feat: Enhance audit trail with created_by and updated_by fields across services

feat(logging): implement structured logging across services

feat(database): Add comprehensive PostgreSQL connection management and configuration

chore(config): Update PostgreSQL URI configuration to support DATABASE_URL environment variable

feat(staff): Implement PostgreSQL integration for staff management and add validation schemas

feat(po-grn): Implement unified PO/GRN endpoints with decimal serialization fix

feat: Add database management script and requirements