Fix FilePathSource/FilePathTarget not working in server-side environments using CJS (closes #360)

src/target.ts

@@ -692,12 +692,18 @@ export class FilePathTarget extends Target {
 			throw new TypeError('options must be an object.');
 		}
 
+		if (!node.getFs) {
+			throw new Error(
+				'FilePathTarget is only available in server-side environments (Node.js, Bun, Deno).',
+			);
+		}
+
 		super();
 
 		// Let's back this target with a StreamTarget, makes the implementation very simple
 		const writable = new WritableStream<StreamTargetChunk>({
 			start: async () => {
-				this._fileHandle = await node.fs.open(filePath, 'w');
+				this._fileHandle = await (await node.getFs()).open(filePath, 'w');
 			},
 			write: async (chunk) => {
 				assert(this._fileHandle);