fix(dashboard): Active Commitments card shows estimated savings as '/mo committed' #1709

What happens

Home > Active Commitments KPI card shows a count with the detail line "$X/mo committed". The figure is not committed spend:

• frontend/src/dashboard.ts:430 renders `${formatCurrency(data.committed_monthly)}/mo committed`.
• committed_monthly is built in calculateCommitmentMetrics (internal/api/handler_dashboard.go:718-733) as the sum of aggregateActiveCommitmentsPerService (:640-650), which adds up each active purchase's EstimatedSavings: monthly savings, not the monthly cost of the commitments.

So the main page states a savings figure as if it were commitment spend. For a typical commitment the two differ several-fold, and a reader comparing it with their bill gets the wrong idea of how much is committed.

Expected

Either:

• relabel the detail line to say what it is (for example "$X/mo estimated savings"), and consider renaming the API field (committed_monthly) so future readers don't repeat the mistake; or
• if the card is meant to show committed spend, compute it from the commitments' cost (upfront amortized plus recurring) instead.

Actual

"$X/mo committed" shows the active commitments' estimated monthly savings.

Notes

• This is a separate defect from ux(frontend): Home savings figures disagree and the trend empty state hides existing history #1686 and from what fix(dashboard): say what Home's savings figures and empty states mean #1707 fixes. fix(dashboard): say what Home's savings figures and empty states mean #1707 relabels the YTD Savings card as an estimate; this card's caption is untouched there.
• Found during the cold review of fix(dashboard): say what Home's savings figures and empty states mean #1707. Production UI, read-only; values omitted on purpose.