migrate to maintained Playwright Go driver

[alixander]

Summary

• move from the retired playwright-community module path to github.com/mxschmitt/playwright-go v0.6100.0
• align Docker Playwright with embedded CLI 1.61.1
• update the Chromium install prompt to 149.0.7827.55

This is the first upstream release that assembles its driver from playwright-core npm plus nodejs.org instead of the retired driver CDN.

Validation

• go mod verify and go mod tidy -diff
• focused tests and compile-all checks
• focused vet
• isolated init-playwright install and launch
• real PNG and animated GIF render smokes
• linux amd64 and arm64 cross-builds

Residual risk

Chromium 149 may change raster output. No fixture files were changed. Existing chain_icon_import and unsigned-commit failures are unrelated baseline issues.