Fix react-hooks lint errors in frontend App.jsx

`npm run lint` in `frontend/` currently fails with 2 errors in `App.jsx`: - `react-hooks/immutability` around line 285 (a `run` callback referenced before/after its own declaration in a `useEffect`) - `react-hooks/set-state-in-effect` at line 516 (`setVisLines` called synchronously inside a `useEffect` body, which can cause cascading renders) These are currently non-blocking in CI (`.github/workflows/ci.yml` runs lint with `continue-on-error: true`) specifically because of this issue. Fixing them would let CI enforce lint on frontend PRs. Run `cd frontend && npm run lint` to reproduce.