Add section 8.4 to SPECIFICATION.md describing the flat BOM flattening
and assembly cost roll-up endpoints with example request/response JSON.
- GET /api/items/{pn}/bom/flat — consolidated leaf parts with
rolled-up quantities and cycle detection
- GET /api/items/{pn}/bom/cost — per-line extended costs and total
assembly cost using standard_cost
Update endpoint count from 74 to 76 in SPECIFICATION.md and README.md.
Add checklist entries for flat BOM and assembly costing features.
3704adb584