Usage while free is shown at cost; agents get rustfmt and clippy
The sidebar's "Usage this month" and the usage page summed what was charged. While g1t is free every charge is zero, so both stopped at what had been charged before free mode began, with the margin in it, and every run since showed as nothing: $6.01 against $6.48 of real use, and further below the AI Gateway's own estimate. Billing now reports usedMicros, what the runs cost on g1t's models and the workspace's own provider together, and measures the breakdowns at cost while free. The card and the usage page show "Used", at cost, and say nothing is charged and credit is not drawn down. The runner image installed Rust with the minimal profile, which has no rustfmt or clippy, so an agent could not format or lint its change and first heard about it from a failed workflow (hello's #85: Formatting failed, the agent was sent back and fixed it). Both are installed now. docs/DEMO.md is rewritten for what g1t is today: GitHub Actions from .g1t/workflows, an agent writing a CI step (#80/#81), an agent sent back by a failed workflow and fixing it (#84/#85), and the merge queue testing combinations with merge_group.
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