Retrieves a single utility bill from the project with a freshly-minted presigned file_url. The download URL expires after 24 hours; re-call this endpoint to refresh it.

Last-parse-wins semantics. Only the most recently uploaded bill on the project feeds its load profile and consumption data. A bill returned by this endpoint that is not the most recent is a historical artifact — it remains in storage but is not currently being used by Aurora to compute consumption.