Adds a shared git hook (.githooks/pre-commit) that lints staged frontend JS/JSX
and blocks the commit on ESLint ERRORS only (warnings allowed). It exits early
for commits with no frontend JS/JSX (backend, SCSS, docs), so it never disrupts
those. Enable once per clone: `git config core.hooksPath .githooks` (or
`sh frontend/setup-hooks.sh`).
Chose a committed .githooks script over husky/lint-staged: this is a monorepo
(git root has the Python backend; only frontend/ is a node package with no root
package.json), so a dependency-free hook avoids an npm-install-time git-config
mutation and keeps backend committers unaffected. Documented in AGENTS.md.
Tested: blocks a staged file with a parse error (exit 123), passes when clean.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
