docs(m177): flag the issue-time run debit — the billing doc contradicts the spec

Spec §2 decides the issue-time floor-token estimate on the grounds that the
spec and data_flow.md §C agree. billing_and_provider_keys.md — the document
that owns billing — records the opposite and names the milestone that changed
it: M80_010 replaced the one-shot lease-issue estimate with per-renewal
metering, and deleted refund-on-actual as unnecessary.

Not paperwork. The estimate has nowhere to land: balance_nanos is read-only on
this path, 'stage' is owned by the renewal accumulator whose ON CONFLICT adds
each slice on top of whatever is there, and a third charge type breaks the
two-rows-per-event invariant. Written as 'stage' it is a double charge.

Parked as a judgment flag rather than built or silently skipped.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>