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/Aws3/GuzzleHttp/Handler/CurlHandler.php

@@ -0,0 +1,43 @@
+<?php
+
+namespace DeliciousBrains\WP_Offload_Media\Aws3\GuzzleHttp\Handler;
+
+use DeliciousBrains\WP_Offload_Media\Aws3\GuzzleHttp\Promise\PromiseInterface;
+use DeliciousBrains\WP_Offload_Media\Aws3\Psr\Http\Message\RequestInterface;
+/**
+ * HTTP handler that uses cURL easy handles as a transport layer.
+ *
+ * When using the CurlHandler, custom curl options can be specified as an
+ * associative array of curl option constants mapping to values in the
+ * **curl** key of the "client" key of the request.
+ *
+ * @final
+ */
+class CurlHandler
+{
+    /**
+     * @var CurlFactoryInterface
+     */
+    private $factory;
+    /**
+     * Accepts an associative array of options:
+     *
+     * - handle_factory: Optional curl factory used to create cURL handles.
+     *
+     * @param array{handle_factory?: ?CurlFactoryInterface} $options Array of options to use with the handler
+     */
+    public function __construct(array $options = [])
+    {
+        $this->factory = $options['handle_factory'] ?? new CurlFactory(3);
+    }
+    public function __invoke(RequestInterface $request, array $options) : PromiseInterface
+    {
+        if (isset($options['delay'])) {
+            \usleep($options['delay'] * 1000);
+        }
+        $easy = $this->factory->create($request, $options);
+        \curl_exec($easy->handle);
+        $easy->errno = \curl_errno($easy->handle);
+        return CurlFactory::finish($this, $easy, $this->factory);
+    }
+}