PR #1337 - Subscription Cost Amortization and True-Up

The Broader Goal at the End of the Previous PR

The cost ledger needed to distinguish the commercial value of tokens from the cash actually spent on a harness plan.

What This PR Shipped

Issue #787 adds harness_billing configuration for subscription, metered, and zero-cost harnesses. Subscription calls amortize a monthly base fee over projected or prior-month throughput, while optional extra usage is charged at the model's metered rates and bounded by a configured cap. Local inference records zero realized cash outlay while retaining API-equivalent value.

The new synlynk cost true-up command reconciles a billing month against the recorded ledger and writes an auditable true_up_reconciliation row. Unit tests cover configuration defaults, amortization, local zero-cost behavior, and under-usage reconciliation.

What This Achieved on the Path to Autonomy

Dispatch economics can now be evaluated using realized cash outlay without losing the comparable API-equivalent benchmark, making harness selection and monthly budgeting more trustworthy.

Strategic Note: The Goal at the End of This PR

The ledger is now ready to compare planned subscription economics with actual provider invoices at the end of each billing cycle.