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/Internal/DiffElem.php

@@ -0,0 +1,31 @@
+<?php declare(strict_types=1);
+
+namespace PhpParser\Internal;
+
+/**
+ * @internal
+ */
+class DiffElem {
+    public const TYPE_KEEP = 0;
+    public const TYPE_REMOVE = 1;
+    public const TYPE_ADD = 2;
+    public const TYPE_REPLACE = 3;
+
+    /** @var int One of the TYPE_* constants */
+    public int $type;
+    /** @var mixed Is null for add operations */
+    public $old;
+    /** @var mixed Is null for remove operations */
+    public $new;
+
+    /**
+     * @param int $type One of the TYPE_* constants
+     * @param mixed $old Is null for add operations
+     * @param mixed $new Is null for remove operations
+     */
+    public function __construct(int $type, $old, $new) {
+        $this->type = $type;
+        $this->old = $old;
+        $this->new = $new;
+    }
+}