Set up stable screenshot visual diffing for pixel-level regression comparisons in Playwright

Steps

1. Use Playwright's built-in `expect(page).toHaveScreenshot('name.png')` assertion — on first run it creates the baseline; on subsequent runs it compares and fails if the diff exceeds the threshold.
2. Commit baseline screenshots to source control alongside test files so reviewers can inspect visual changes and CI uses the same baselines as local development.
3. Configure a pixel-difference threshold and/or maximum diff pixel count in `playwright.config.ts` under `expect.toHaveScreenshot` to tolerate sub-pixel anti-aliasing differences: `{ threshold: 0.2, maxDiffPixelRatio: 0.01 }`.
4. Mask dynamic regions (timestamps, avatars, ads) with `mask: [page.getByTestId('timestamp')]` option on `toHaveScreenshot` to exclude them from comparison.
5. Generate and update baselines in CI using `npx playwright test --update-snapshots` when an intentional UI change is landed, then commit the new baseline images.