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/sebastian/diff/src/Chunk.php

@@ -0,0 +1,89 @@
+<?php declare(strict_types=1);
+/*
+ * This file is part of sebastian/diff.
+ *
+ * (c) Sebastian Bergmann <sebastian@phpunit.de>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+namespace SebastianBergmann\Diff;
+
+final class Chunk
+{
+    /**
+     * @var int
+     */
+    private $start;
+
+    /**
+     * @var int
+     */
+    private $startRange;
+
+    /**
+     * @var int
+     */
+    private $end;
+
+    /**
+     * @var int
+     */
+    private $endRange;
+
+    /**
+     * @var Line[]
+     */
+    private $lines;
+
+    public function __construct(int $start = 0, int $startRange = 1, int $end = 0, int $endRange = 1, array $lines = [])
+    {
+        $this->start      = $start;
+        $this->startRange = $startRange;
+        $this->end        = $end;
+        $this->endRange   = $endRange;
+        $this->lines      = $lines;
+    }
+
+    public function getStart(): int
+    {
+        return $this->start;
+    }
+
+    public function getStartRange(): int
+    {
+        return $this->startRange;
+    }
+
+    public function getEnd(): int
+    {
+        return $this->end;
+    }
+
+    public function getEndRange(): int
+    {
+        return $this->endRange;
+    }
+
+    /**
+     * @return Line[]
+     */
+    public function getLines(): array
+    {
+        return $this->lines;
+    }
+
+    /**
+     * @param Line[] $lines
+     */
+    public function setLines(array $lines): void
+    {
+        foreach ($lines as $line) {
+            if (!$line instanceof Line) {
+                throw new InvalidArgumentException;
+            }
+        }
+
+        $this->lines = $lines;
+    }
+}