feat: Http curl wrapper and TokenStore with atomic write and flock

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

src/HttpClient.php

@@ -0,0 +1,17 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Weerscherm;
+
+interface HttpClient
+{
+    /**
+     * @param array<string, string|int|float> $query
+     * @param list<string> $headers
+     */
+    public function get(string $url, array $query = [], array $headers = []): HttpResponse;
+
+    /** @param array<string, string|int|float> $fields */
+    public function postForm(string $url, array $fields): HttpResponse;
+}