Use Playwright-managed Chromium for devtools

[cbusillo]

Summary

• Replace the xtradeb Launchpad PPA Chromium install in runtime-devtools with pinned Playwright-managed Chromium.
• Set CHROME_BIN to /usr/local/bin/chromium-playwright and update the devtools smoke test fallback path.
• Document the Playwright-managed Chromium contract in README.

Refs #23

Why

The xtradeb PPA endpoint has been timing out (ppa.launchpadcontent.net:443), leaving main red even for docs-only changes. Playwright provides multi-arch Chromium downloads with CDN fallbacks and avoids Ubuntu Snap-in-Docker issues.

Local Validation

• git diff --check
• shellcheck scripts/smoke-devtools.sh
• actionlint .github/workflows/*.yml
• jq empty .github/github-repo-workflow.json
• docker build -t odoo-docker:verify-devtools-playwright --target runtime-devtools .
• scripts/smoke-devtools.sh odoo-docker:verify-devtools-playwright
• docker build --platform linux/amd64 -t odoo-docker:verify-devtools-playwright-amd64 --target runtime-devtools .
• scripts/smoke-devtools.sh odoo-docker:verify-devtools-playwright-amd64
• docker run --rm --platform linux/amd64 --entrypoint /bin/bash odoo-docker:verify-devtools-playwright-amd64 -lc 'test -x "${CHROME_BIN}" && "${CHROME_BIN}" --version && readlink -f "${CHROME_BIN}"'\n\n## Notes\n- Local arm64 image inspected at about 1.0 GB.\n- Playwright downloads Chromium plus its ffmpeg helper; only Chromium is exposed through CHROME_BIN.\n- The Chromium executable directory differs by architecture (chrome-linux on arm64, chrome-linux64 on amd64), so the Dockerfile discovers either path.