Update Theme Watch Process to cover all of CSS, JS, images and fonts

[dipakmdhrm]

Closes #324

Summary

Replaces the PHP/Robo-based theme compilation pipeline with npm scripts, simplifying the build
toolchain and enabling parallel asset watching.

Changes:

• package.json: Add build and watch npm scripts for CSS, JS, fonts, and images. Add
  concurrently, chokidar-cli, and imagemin-cli as dev dependencies
• ThemeTrait.php: Remove complex PHP-based asset handling (JS minification, image optimization, SVG
  compression, file watching). Delegate all of this to npm run build
• ddev theme:compile: Now runs npm install && npm run build directly instead of ddev robo theme:compile
• ddev theme:watch: Now runs npm run watch which uses concurrently to watch CSS, JS, fonts, and
  images in parallel
• config.local.yaml.example / README.md: Update references from ddev robo theme:compile[-debug]
  to ddev theme:compile

Test plan

• ddev theme:compile builds all assets to dist/ (CSS, JS, fonts, images)
• ddev theme:watch starts watchers for all asset types in parallel
• ddev restart triggers theme compilation via the updated hook
• ddev phpcs and ddev phpstan pass (verified by pre-push hook)
• Theme compilation during deployment (PHP robo leveraging npm) works properly

theme-2026-03-12_14.33.38.mp4

[AronNovak]

@dipakmdhrm This is nice!

I have #995, but I am happy to throw it away, the only thing I'd like to double-check that the process should exit with non-zero code if CSS or JS or any other asset has a failure, so the process has a glitch, like malformed SVG, broken JS, syntax error in the style, etc.

[dipakmdhrm]

@dipakmdhrm This is nice!

I have #995, but I am happy to throw it away, the only thing I'd like to double-check that the process should exit with non-zero code if CSS or JS or any other asset has a failure, so the process has a glitch, like malformed SVG, broken JS, syntax error in the style, etc.

CSS and SVGs had proper exit logic (compile fail on error), but it wasn't so for JS. I've replaced minify (which always gives exit code 0), with terser for proper exit logic.

[AronNovak]

@dipakmdhrm Thanks! Now minify has the proper exit code handling in the latest release, but terser has much bigger user base actually!

[AronNovak]

Looks promising for me!