ADX dashboard: List cost / Commitment savings don't match between Summary and Rate Optimization pages

🤖 [AI] Filed from findings raised in discussion #2068.

⚠️ Problem

The ADX dashboard's Summary page and Rate Optimization page show different "List cost" and "Commitment savings" numbers for the same month (reported gap: ~5.7% on List cost, ~2x on Commitment savings). Confirmed independently by two customers.

🛠️ Solution

Root cause, verified against src/templates/finops-hub/dashboard.json:

• Summary page's "Cost summary" tile (query 5ff29428…) and "Summary"/"Savings summary" tiles (e8b343dc…, f5f240a8…) compute List/Contracted/Effective cost and Commitment savings as a flat sum(ListCost)/sum(ContractedCost)/sum(EffectiveCost) over CostsByMonth/CostsByDay — with no exclusion of ChargeCategory == 'Purchase' rows.
• Rate Optimization page's equivalent tiles (e17346d1…, 3b3f0a58…) already carry where x_AmortizationClass != 'Principal' — explicitly commented "Don't double-count commitment discount purchases."

A Reservation/Savings Plan upfront purchase row carries the full ListCost/ContractedCost with EffectiveCost ≈ 0 (the real usage cost is amortized separately). Summing it in unfiltered, as the Summary page does, inflates that month's List cost and Commitment savings by roughly the purchase amount.

Fix: add the same x_AmortizationClass != 'Principal' exclusion to the three Summary-page queries, mirroring the existing Rate Optimization pattern.

ℹ️ Additional context

• Not a duplicate of #2214/#2286 (different mechanism, already covered by #2248) or #1424/#2176 (wrong savings within Rate Optimization, not cross-page).
• PR #2248 does not fix this — it touches two of the three affected Summary tiles but doesn't add the Purchase-row exclusion, so this will persist even after #2248 merges.
• Small, low-risk, well-scoped fix — no new logic to invent, just apply the existing Rate Optimization pattern to the Summary page.

Related: #2068 (discussion)

Open src/templates/finops-hub/dashboard.json and compare the three Summary-page queries (5ff29428…, e8b343dc…, and f5f240a8…) with the existing Rate Optimization queries (e17346d1… and 3b3f0a58…). Verify that all three Summary queries exclude x_AmortizationClass == 'Principal', then confirm their List cost and Commitment savings calculations no longer include purchase rows.