bug(api/purchases): Total Upfront/Monthly/Annual Savings KPIs include cancelled purchases #736

Symptom (QA row 278, Purchases page > Approval queue step 1.6)

When an admin clicks Cancel on a pending purchase request in the Approval queue:

• Counts for pending and cancelled purchases update correctly.
• BUT Total Upfront Spent, Monthly Saving, and Annual Savings all update as if the cancelled purchase had been approved, adding its committed/saved amounts to the KPIs.

A cancelled purchase represents zero committed spend and zero realized savings. The KPIs must exclude cancelled-status executions.

Reproduction

1. Send a high-cost commitment for approval (so the delta is large and visible).
2. Note the Total Upfront Spent / Monthly Saving / Annual Savings KPIs on the Purchases page.
3. Click Cancel on that pending request in the Approval queue.
4. Observe: pending count -1, cancelled count +1 (correct). But Total Upfront Spent +cost_of_cancelled_purchase, Monthly Saving +its_savings, etc. (wrong — these should stay unchanged.)

Fix direction

Trace the KPI aggregation:

• Likely a backend handler that sums all execution rows without filtering on status (or status set is too permissive, e.g., status IN ('approved', 'completed', 'cancelled') instead of status IN ('approved', 'completed')).
• Search for "Total Upfront Spent" / "Monthly Saving" / "Annual Savings" in internal/api/ and frontend/src/.
• The cancel-purchase mutation likely transitions to cancelled but doesn't subtract from these aggregates (or the GET handler includes cancelled in the SUM).

Whichever is the data source, exclude status='cancelled' from these three aggregates.

Tests required

• API integration test: create N approved purchases + 1 pending; capture KPI values; cancel the pending; assert KPIs unchanged.
• UI test: same scenario in the browser; assert the displayed numbers don't change after cancellation.

Source of finding

QA verification spreadsheet row 278 (step 1.6 of Approval queue).