Adds two-job CI (backend + frontend) running ruff, pytest (unit only -
skipping heavy ML deps), docker compose config validation for both dev
and prod overlays, plus npm ci -> eslint -> tsc -> vite build for the
frontend.
ESLint config uses the v9 flat-config format that the project was
already on (eslint v9 dropped .eslintrc support); replaces the broken
'eslint . --ext' invocation and adds @typescript-eslint, react-hooks,
and react-refresh plugins.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
