fix: wrong fiat calculations and retrieval

[talvasconcelos]

fix fiat withraw limits being converted in the wrong place.

The frontend was multiplying fiat min/max amounts before sending them to the API, but the backend already handles that normalization. That could save inflated values when updating an existing link.

The LNURL flow now uses the shared min_max_withdrawable() helper when exposing withdraw limits and when validating callback invoice amounts. That keeps min/max handling consistent for both sat and fiat links, removes duplicated fiat conversion logic, and makes the min/max limits match the amount validation path.

It also updates the uv dev dependency config to the newer dependency group format and refreshes the lockfile.