Modularize plugin, drop deps, align with laravel-vite-plugin

[gcavanunez]

Goal

Stop wrapping laravel-vite-plugin and port the vite pieces that Jigsaw actually needs into this plugin directly. Keep the public jigsaw(config) API stable.

How to test

npm install
npm run build
npm test

End-to-end smoke test

1. Clone this branch and build the plugin:

git clone -b gc/standalone-v2 git@github.com:tighten/jigsaw-vite-plugin.git
cd jigsaw-vite-plugin && npm install && npm run build

2. Create a Jigsaw project beside it:

composer create-project tightenco/jigsaw ../test-site
cd ../test-site

3. Point the plugin at this branch and bump Vite to 8:

npm install --save-dev "file:../jigsaw-vite-plugin" "vite@^8.0.0"

4. Verify:
   • npm run build: source/assets/build/manifest.json static site appears under build_production
   • npm run dev: banner prints JIGSAW plugin v2.0.0, the hot file is written before the initial build.
   • Refresh: editing source/**/*.md or source/**/*.php triggers a rebuild followed by a full-page reload.

[nicodevs]

Tested this with many Jigsaw projects, works as expected. Great job! 🙌