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/symfony/stopwatch/StopwatchPeriod.php

@@ -0,0 +1,73 @@
+<?php
+
+/*
+ * This file is part of the Symfony package.
+ *
+ * (c) Fabien Potencier <fabien@symfony.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Symfony\Component\Stopwatch;
+
+/**
+ * Represents an Period for an Event.
+ *
+ * @author Fabien Potencier <fabien@symfony.com>
+ */
+class StopwatchPeriod
+{
+    private int|float $start;
+    private int|float $end;
+    private int $memory;
+
+    /**
+     * @param int|float $start         The relative time of the start of the period (in milliseconds)
+     * @param int|float $end           The relative time of the end of the period (in milliseconds)
+     * @param bool      $morePrecision If true, time is stored as float to keep the original microsecond precision
+     */
+    public function __construct(int|float $start, int|float $end, bool $morePrecision = false)
+    {
+        $this->start = $morePrecision ? (float) $start : (int) $start;
+        $this->end = $morePrecision ? (float) $end : (int) $end;
+        $this->memory = memory_get_usage(true);
+    }
+
+    /**
+     * Gets the relative time of the start of the period in milliseconds.
+     */
+    public function getStartTime(): int|float
+    {
+        return $this->start;
+    }
+
+    /**
+     * Gets the relative time of the end of the period in milliseconds.
+     */
+    public function getEndTime(): int|float
+    {
+        return $this->end;
+    }
+
+    /**
+     * Gets the time spent in this period in milliseconds.
+     */
+    public function getDuration(): int|float
+    {
+        return $this->end - $this->start;
+    }
+
+    /**
+     * Gets the memory usage in bytes.
+     */
+    public function getMemory(): int
+    {
+        return $this->memory;
+    }
+
+    public function __toString(): string
+    {
+        return \sprintf('%.2F MiB - %d ms', $this->getMemory() / 1024 / 1024, $this->getDuration());
+    }
+}