wow... so much yak shaving, including priceless bits like "sat with ChatGPT for a bit [...] we came up with OurCar" (I mean... how original is that, clearly powerful datacenters computing over a dump of the Internet was needed), I'm impressed. All this to avoid doing one subtraction (km before, km now) then multiplication (result times average litter/km) in your head. That's a LOT of effort to be lazy.
FWIW if I were to do this I'd do echo > index.html to make it available to anyone, Worldwide, for free! For the fancy version I'd make priceperlitterperkm URL parameter to make it work not just for my area. But that's like an entire additional like of code. My point being... I'd make a Web page, on app, no deployment, no tracking.
ssh homeserver 'echo hi >> /var/www/self-published/index.html' and voila. I'll probably share my gist this way from the CLI.
ssh homeserver "echo '$(ls)' >> /var/www/self-published/index.html" if I want to run a command locally first, not on homeserver (notice the " vs ').