- Add dtos package with request/response structs
- Add repositories: Material, Filament, Printer, PrintJob, UsageLog
- Add services: FilamentService, PrinterService, PrintJobService
- Add handlers for all 5 resources with consistent error responses
- Wire all endpoints into Chi router under /api
- Validation on POST/PUT filament endpoints
- Filter/pagination support on list endpoints
- Soft-delete for filaments (DELETE /api/filaments/{id})
- go build ./... && go vet ./... → PASS
