oci_bom_gen.py from_spec now reads metadata.discount_pct as fallback
when individual line items don't specify a discount. This means
discount_pct: 0.45 in the spec metadata applies 45% to every SKU.
Previously, global discount was silently ignored — only per-item
discount fields were read (defaulting to 0.0).
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>