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/Proxy.php

@@ -0,0 +1,49 @@
+<?php
+
+namespace DeliciousBrains\WP_Offload_Media\Aws3\GuzzleHttp\Handler;
+
+use DeliciousBrains\WP_Offload_Media\Aws3\GuzzleHttp\Promise\PromiseInterface;
+use DeliciousBrains\WP_Offload_Media\Aws3\GuzzleHttp\RequestOptions;
+use DeliciousBrains\WP_Offload_Media\Aws3\Psr\Http\Message\RequestInterface;
+/**
+ * Provides basic proxies for handlers.
+ *
+ * @final
+ */
+class Proxy
+{
+    /**
+     * Sends synchronous requests to a specific handler while sending all other
+     * requests to another handler.
+     *
+     * @param callable(\Psr\Http\Message\RequestInterface, array): \GuzzleHttp\Promise\PromiseInterface $default Handler used for normal responses
+     * @param callable(\Psr\Http\Message\RequestInterface, array): \GuzzleHttp\Promise\PromiseInterface $sync    Handler used for synchronous responses.
+     *
+     * @return callable(\Psr\Http\Message\RequestInterface, array): \GuzzleHttp\Promise\PromiseInterface Returns the composed handler.
+     */
+    public static function wrapSync(callable $default, callable $sync) : callable
+    {
+        return static function (RequestInterface $request, array $options) use($default, $sync) : PromiseInterface {
+            return empty($options[RequestOptions::SYNCHRONOUS]) ? $default($request, $options) : $sync($request, $options);
+        };
+    }
+    /**
+     * Sends streaming requests to a streaming compatible handler while sending
+     * all other requests to a default handler.
+     *
+     * This, for example, could be useful for taking advantage of the
+     * performance benefits of curl while still supporting true streaming
+     * through the StreamHandler.
+     *
+     * @param callable(\Psr\Http\Message\RequestInterface, array): \GuzzleHttp\Promise\PromiseInterface $default   Handler used for non-streaming responses
+     * @param callable(\Psr\Http\Message\RequestInterface, array): \GuzzleHttp\Promise\PromiseInterface $streaming Handler used for streaming responses
+     *
+     * @return callable(\Psr\Http\Message\RequestInterface, array): \GuzzleHttp\Promise\PromiseInterface Returns the composed handler.
+     */
+    public static function wrapStreaming(callable $default, callable $streaming) : callable
+    {
+        return static function (RequestInterface $request, array $options) use($default, $streaming) : PromiseInterface {
+            return empty($options['stream']) ? $default($request, $options) : $streaming($request, $options);
+        };
+    }
+}