I installed this as a PWA on my Pixel, and for some reason it keeps auto-rotating (to landscape mode), despite having disabled auto-rotation on my phone.

Is it something you intentionally want or need? It makes it impossible for me to read in bed.

good catch, fixed: orientation: 'any' was meant as 'don't lock the phone' and android treated it the exact opposite. removed it

sadly it may take a bit for your phone to pick up the new manifest, an uninstall and reinstall might fix it