End-to-end browser tests that run against the built pi-web binary across desktop, mobile, and iPad viewports.

make e2e-setup   # one-time: install deps + browsers
make e2e         # build binary + run the full suite

See docs/dev/e2e-testing.md for the full guide: project matrix, scripted server lifecycle, sanitized fixtures, the stub pi, CI, and how to add tests.