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/nikic/php-parser/lib/PhpParser/Node/Scalar/EncapsedStringPart.php

@@ -0,0 +1,17 @@
+<?php declare(strict_types=1);
+
+namespace PhpParser\Node\Scalar;
+
+use PhpParser\Node\InterpolatedStringPart;
+
+require __DIR__ . '/../InterpolatedStringPart.php';
+
+if (false) {
+    /**
+     * For classmap-authoritative support.
+     *
+     * @deprecated use \PhpParser\Node\InterpolatedStringPart instead.
+     */
+    class EncapsedStringPart extends InterpolatedStringPart {
+    }
+}