Motivation

• Provide a reproducible, automated benchmark harness to compare this viewer against other diff viewer libraries across large file sizes and runtime metrics.
• Collect actionable performance metrics (FPS, initial render time, memory) for datasets up to 100k lines to guide optimization and regressions.

Description

• Add a new apps/benchmark Vite app with src/main.tsx, index.html, tsconfig.json, vite.config.ts, and a package manifest to host multiple diff viewer implementations for side-by-side benchmarking.
• Add scripts/run-benchmark.mjs, a Playwright-driven runner that starts the dev server, auto-installs Playwright Chromium if needed, visits benchmark cases for multiple libraries and input sizes, handles per-case timeouts (60s), and emits benchmark-results/results.json and benchmark-results/results.md.
• Expose a root pnpm benchmark script in package.json and add playwright as a dev dependency, and update README.md and CHANGELOG.md with usage and changelog entries for 0.1.3.
• The benchmark app supports optional fallback for react-diff-viewer-continued and records timeout cases instead of failing the whole run, and the runner ensures the dev server is stopped cleanly after execution.

Testing

• No automated tests were executed as part of this change; to run the benchmark locally use pnpm benchmark, which runs the Vite app and a headless Chromium session and writes results to benchmark-results/.

Codex Task