Initial commit: Site Builder with PHP API backend

Visual drag-and-drop website builder using GrapesJS with:
- Multi-page editor with live preview
- File-based asset storage via PHP API (no localStorage base64)
- Template library, Docker support, and Playwright test suite

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

router.php

@@ -0,0 +1,33 @@
+<?php
+/**
+ * PHP Built-in Server Router
+ *
+ * Usage: php -S localhost:8081 router.php
+ *
+ * Routes /api/* requests to api/index.php and serves all other
+ * requests as static files (same behavior as Apache with .htaccess).
+ */
+
+$uri = parse_url($_SERVER['REQUEST_URI'], PHP_URL_PATH);
+
+// Route API requests to the API handler
+if (strpos($uri, '/api/') === 0) {
+    require __DIR__ . '/api/index.php';
+    return true;
+}
+
+// Serve static files as-is
+$filePath = __DIR__ . $uri;
+if ($uri !== '/' && is_file($filePath)) {
+    return false; // Let PHP's built-in server handle the file
+}
+
+// Default: serve index.html for directory requests
+if (is_dir($filePath)) {
+    $indexPath = rtrim($filePath, '/') . '/index.html';
+    if (is_file($indexPath)) {
+        return false;
+    }
+}
+
+return false;