Summary

• Update vendored jQuery UI from 1.14.1 to 1.14.2.
• Rebuild every theme jquery-ui.css file on the 1.14.2 shared structure while preserving each theme's existing ThemeRoller colors and shadow settings.
• Replace deprecated local buttonset() calls with controlgroup() now that jQuery UI 1.14.2 no longer enables the backcompat path by default.
• Add Playwright smoke coverage for the jQuery UI controlgroup() path.

Notes

• jQuery core stays at 3.7.1 in this PR. jQuery 4.0.0 is current, but it is a major release with breaking removals and should be handled as a separate migration with broader plugin testing.
• The jQuery UI assets were pulled from the official 1.14.2 distribution.

Testing

• node --check include/js/jquery-ui.js
• node --check include/layout.js
• node --check include/themes/dark/main.js
• node --check include/themes/modern/main.js
• node --check tests/e2e/jquery-smoke.spec.js
• git diff --check
• rg checks for stale jQuery UI versions, deprecated buttonset() calls, and old IE-only CSS compatibility lines

Not run locally:

• npx --no-install playwright test tests/e2e/jquery-smoke.spec.js could not run because Playwright is not installed in this worktree; npx --no-install attempted npm registry access and failed under restricted network.