feat: project skeleton with Config and exceptions

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

src/NetatmoAuthException.php

@@ -0,0 +1,10 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Weerscherm;
+
+/** De Netatmo-koppeling is verlopen: de refresh token is ongeldig. Herstel via bin/netatmo-init.php. */
+final class NetatmoAuthException extends UpstreamException
+{
+}