Small display issue with footprint in tons

Just letting you know that there seems to be a typo in line 16 of frontend/helpers.py for the order of magnitude when the footprint is larger than 1e6: 

`        text_footprint = f"{footprint_g / 1e3:,.0f} T{co2e}"`

As the footprint is initially in grams, this should probably be something like:

`        text_footprint = f"{(footprint_g / 1e6):,.3f} T{co2e}"`