Finance – Add operational deficit as a new metric

LPC themselves have committed to getting this to 0.

This is challenging because its a made up metric and the government doesn't track it.

This is different from the Public Accounts _operating_ deficit.

The LPC promise is about operational vs capital spending. (employee time vs capital formation)

The issue names no file, test, or entry point, so first inspect the repository to find how existing finance metrics are defined and displayed. Clarify the operational-versus-capital spending inputs and the intended calculation, then add the metric with coverage demonstrating the agreed definition and its distinction from the Public Accounts operating deficit.

Written by the indexing model from the issue text.