Rebase resolution: dev's #392 introduced tests_backend/requirements.txt
(python 3.14, phcc 0.13.357, homeassistant 2026.8.3) — exactly the
single-source-of-pins AC of this issue, so the duplicate
requirements_test.txt is dropped and both workflows keep installing from
the #392 file; ruff is added there for the lint step. The backend
reuse key no longer names the dead file (tests_backend/ as a root
already covers the new one); ARCHITECTURE.md points at the real path.
User-Visible: no
Issue: #42
Codex
569867487c