Add set-once IsAddOn with server cutoff at create, board DTO exposure, legacy type-7 backfill, and Types=AddOn search compat. Aligns with FE PR #61 frozen contract.
Persist primary/extra services, service notes, free-text POC, and
tech/vendor notes on create/patch/board/detail instead of embedding
them in description.
Expose POST /api/workorders/board and POST /api/workorders/{id}/cancel for SHOC wizard/inline creation and soft cancel, with field locks, WO# normalization, and Admin-only hard delete.