T2.1: Renamed warehouse_type -> construction_warehouse_type
in almacenes_proyecto to avoid naming conflict with ERP-Core
T2.3: Added user_id column to hr.employees
- Optional FK to auth.users (employee may not have system access)
- Unique constraint for 1:1 mapping
- Conditional FK (only created if auth.users exists)
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>