070: Every run costed: the platform's own cost and tokens for each scheduled run, on the costs page

Scenario

Given the scheduled runs of the desks and the newsroom
When the accountant reads each run's session usage and final result
Then admin/build/wire-runs.json holds a row per run: when, the task, the cost and the tokens per model, the turns, the subagents, what the permission check refused (by kind, never the command's arguments) and what it published
And the costs page shows the runs by task, by model and one by one, with the working sessions that built the wires counted apart

Outcome

Shipped in v0.12.74: admin/build/runs_ledger.py (adds a run, refuses a row shaped like a key), admin/build/wire-runs.json with the runs of 14 to 16 October, and the runs section of wire/costs.html. Kept current by the accountant (card 071).