rewrite Playwright visual regression tests

Rewrite canvas snapshot tests for the new demo UI. Split the single
monolithic test into 8 focused tests: default render, zoom, resize,
rotation (180/90/120), border radius, and exported image. Also test
that getImageScaledToCanvas produces a clean image without color
overlay (#420). Add Playwright to CI pipeline.

Author: mosch

.github/workflows/test.yml

@@ -49,3 +49,9 @@ jobs:
 
       - name: Unit tests (lib)
         run: pnpm --filter react-avatar-editor test
+
+      - name: Install Playwright browsers
+        run: pnpm --filter react-avatar-editor exec playwright install --with-deps chromium
+
+      - name: Visual regression tests
+        run: pnpm --filter react-avatar-editor exec playwright test