feat: add php generator stub

Author: dmitriyeff

src/generators/php/index.ts

@@ -0,0 +1,7 @@
+import type { Generator, GeneratorOptions } from '../interface.js';
+
+export const phpGenerator: Generator = {
+  async generate(_outputDir: string, _options: GeneratorOptions): Promise<void> {
+    throw new Error('PHP generator is not yet implemented');
+  },
+};