- Create DropdownOption model with Category, Value, ParentValue for Trade/SubTrade/Problem
- Add DropdownOptionsController with CRUD + ByCategory endpoint with parent filtering
- Add Problem, Trade, SubTrade, VendorNTE, ScheduledDate, CompletedDate, Source to WorkOrder
- Update EditWorkorder_DTO and GetWorkorderById with new fields
- Audit log tracks changes to all new fields
- Seed default Trades (10), SubTrades (20), and Problems (11) on startup