feat: add Go, PHP, and Laravel SDKs

- Go SDK: zero deps, functional options pattern, full endpoint coverage
- PHP SDK: PHP 8.1+, curl-based, PdfOptions class, PSR-4 autoloading
- Laravel package: ServiceProvider, Facade, config publishing
- All SDKs document complete PDF options including new v0.4.5 params

sdk/php/src/DocFastException.php

@@ -0,0 +1,18 @@
+<?php
+
+declare(strict_types=1);
+
+namespace DocFast;
+
+class DocFastException extends \RuntimeException
+{
+    public readonly int $statusCode;
+    public readonly ?string $errorCode;
+
+    public function __construct(string $message, int $statusCode, ?string $errorCode = null, ?\Throwable $previous = null)
+    {
+        $this->statusCode = $statusCode;
+        $this->errorCode = $errorCode;
+        parent::__construct($message, $statusCode, $previous);
+    }
+}