feat: add S3-compatible storage provider (MinIO, Ceph, R2, etc.)

Adds a new 'S3-Compatible Storage' provider that works with any
S3-API-compatible object storage service, including MinIO, Ceph,
Cloudflare R2, Backblaze B2, and others.

Changes:
- New provider class: classes/providers/storage/s3-compatible-provider.php
  - Provider key: s3compatible
  - Reads user-configured endpoint URL from settings
  - Uses path-style URL access (required by most S3-compatible services)
  - Supports credentials via AS3CF_S3COMPAT_ACCESS_KEY_ID /
    AS3CF_S3COMPAT_SECRET_ACCESS_KEY wp-config.php constants
  - Disables AWS-specific features (Block Public Access, Object Ownership)
- New provider SVG icons (s3compatible.svg, -link.svg, -round.svg)
- Registered provider in main plugin class with endpoint setting support
- Updated StorageProviderSubPage to show endpoint URL input for S3-compatible
- Built pro settings bundle with rollup (Svelte 4.2.19)
- Added package.json and updated rollup.config.mjs for pro-only builds

vendor/Gcp/symfony/polyfill-php81/Resources/stubs/CURLStringFile.php

@@ -0,0 +1,45 @@
+<?php
+
+namespace DeliciousBrains\WP_Offload_Media\Gcp;
+
+/*
+ * This file is part of the Symfony package.
+ *
+ * (c) Fabien Potencier <fabien@symfony.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+if (\PHP_VERSION_ID >= 70400 && \extension_loaded('curl')) {
+    /**
+     * @property string $data
+     */
+    class CURLStringFile extends \CURLFile
+    {
+        private $data;
+        public function __construct(string $data, string $postname, string $mime = 'application/octet-stream')
+        {
+            $this->data = $data;
+            parent::__construct('data://application/octet-stream;base64,' . \base64_encode($data), $mime, $postname);
+        }
+        public function __set(string $name, $value) : void
+        {
+            if ('data' !== $name) {
+                $this->{$name} = $value;
+                return;
+            }
+            if (\is_object($value) ? !\method_exists($value, '__toString') : !\is_scalar($value)) {
+                throw new \TypeError('Cannot assign ' . \gettype($value) . ' to property CURLStringFile::$data of type string');
+            }
+            $this->name = 'data://application/octet-stream;base64,' . \base64_encode($value);
+        }
+        public function __isset(string $name) : bool
+        {
+            return isset($this->{$name});
+        }
+        public function &__get(string $name)
+        {
+            return $this->{$name};
+        }
+    }
+}