Improve SKU catalog hygiene and BOM accuracy

- refresh_sku_catalog.py: add --discover to report API SKUs missing from
  catalog, filtered to already-curated serviceCategory values. Auto-runs
  at end of --validate and --refresh so gaps surface on every maintenance
  pass. First run found 162 missing SKUs (Blackwell GPUs, X12 Ax compute,
  VMware reserved tiers, WebLogic-on-OKE, Analytics/OIC BYOL).
- oci_bom_gen.py: fix Cost % column being blank. Back-fill was gated on
  formula detection but data rows write raw numbers, so the predicate
  never matched. Now tracks data_item_rows explicitly.
- .gitea/workflows/sku-catalog-refresh.yaml: monthly automation (1st at
  09:00 UTC). Auto-refresh prices → push branch + open PR; detect new
  SKUs → open issue with labels. Gated on secrets.GITEA_TOKEN.
- kb/pricing/oci-sku-catalog.yaml: add B95714 / B95715 (Autonomous ATP
  Dedicated ECPU, LI + BYOL) — canonical SKUs for ADB-D pricing.
- kb/services/compute.yaml: add X12 family (VM.Standard4.Ax.Flex,
  BM.Standard4.Ax.120), E6.Ax and A4.Ax variants. Verified against
  docs.oracle.com computeshapes.htm. Bump last_verified + changelog.
- templates/bom-spec.yaml: document 730 hrs/month convention as default
  (= real annual billing / 12; 744 overstates by 1.92% on 12-month TCO).
- Makefile: new 'make sku-discover' target.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

templates/bom-spec.yaml

@@ -48,3 +48,4 @@ bom:
   notes:
     - "Pricing based on Ashburn region (OC1)"
     - "Discounts subject to Oracle approval"
+    - "Hours convention — 730 vs 744: this BOM uses 730 hrs/month (= 8,760 annual hrs / 12), which equals the actual yearly OCI billing for hourly SKUs. OCI Cost Estimator defaults to 744 hrs/month (worst-case 31-day month); extrapolated to 12 months, 744 overstates the real annual cost by 1.92%. For 12-month TCO/proposals, 730 is the accurate figure; 744 is only appropriate when quoting a single peak month as an upper bound."