refactor: Cleanup git state - commit all staged changes

Major refactoring cleanup:
- Add new controller architecture (class-controller-*.php)
- Add new settings-v2 UI (views/settings-v2/)
- Add new CSS architecture (agentic-sidebar.css, tokens)
- Add esbuild build pipeline (scripts/build.js, package.json)
- Add composer dependencies (vendor/)
- Add frontend src directory (assets/js/src/index.jsx)
- Add documentation files
- Remove old/obsolete files (class-settings.php, old CSS)

This commits all pending changes from previous refactoring efforts.

vendor/twig/string-extra/README.md

@@ -0,0 +1,21 @@
+String Extension
+================
+
+This package is a Twig extension that provides integration with the Symfony
+String component. It provides the following filters:
+
+ * [`u`][1]: Wraps a text in a `UnicodeString` object to give access to
+[methods of the class][2].
+
+ * [`slug`][3]: Wraps the [`AsciiSlugger`][4]'s `slug` method.
+
+ * [`singular`][5] and [`plural`][6]: Wraps the [`Inflector`][7] `singularize`
+   and `pluralize` methods.
+
+[1]: https://twig.symfony.com/u
+[2]: https://symfony.com/doc/current/components/string.html
+[3]: https://twig.symfony.com/slug
+[4]: https://symfony.com/doc/current/components/string.html#slugger
+[5]: https://twig.symfony.com/singular
+[6]: https://twig.symfony.com/plural
+[7]: https://symfony.com/doc/current/components/string.html#inflector