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/Aws/StreamRequestPayloadMiddleware.php

@@ -0,0 +1,67 @@
+<?php
+
+namespace DeliciousBrains\WP_Offload_Media\Aws3\Aws;
+
+use DeliciousBrains\WP_Offload_Media\Aws3\Aws\Api\Service;
+use DeliciousBrains\WP_Offload_Media\Aws3\Aws\Exception\IncalculablePayloadException;
+use DeliciousBrains\WP_Offload_Media\Aws3\Psr\Http\Message\RequestInterface;
+/**
+ * @internal
+ */
+class StreamRequestPayloadMiddleware
+{
+    private $nextHandler;
+    private $service;
+    /**
+     * Create a middleware wrapper function
+     *
+     * @param Service $service
+     * @return \Closure
+     */
+    public static function wrap(Service $service)
+    {
+        return function (callable $handler) use($service) {
+            return new self($handler, $service);
+        };
+    }
+    public function __construct(callable $nextHandler, Service $service)
+    {
+        $this->nextHandler = $nextHandler;
+        $this->service = $service;
+    }
+    public function __invoke(CommandInterface $command, RequestInterface $request)
+    {
+        $nextHandler = $this->nextHandler;
+        $operation = $this->service->getOperation($command->getName());
+        $contentLength = $request->getHeader('content-length');
+        $hasStreaming = \false;
+        $requiresLength = \false;
+        // Check if any present input member is a stream and requires the
+        // content length
+        foreach ($operation->getInput()->getMembers() as $name => $member) {
+            if (!empty($member['streaming']) && isset($command[$name])) {
+                $hasStreaming = \true;
+                if (!empty($member['requiresLength'])) {
+                    $requiresLength = \true;
+                }
+            }
+        }
+        if ($hasStreaming) {
+            // Add 'transfer-encoding' header if payload size not required to
+            // to be calculated and not already known
+            if (empty($requiresLength) && empty($contentLength) && isset($operation['authtype']) && $operation['authtype'] == 'v4-unsigned-body') {
+                $request = $request->withHeader('transfer-encoding', 'chunked');
+                // Otherwise, make sure 'content-length' header is added
+            } else {
+                if (empty($contentLength)) {
+                    $size = $request->getBody()->getSize();
+                    if (\is_null($size)) {
+                        throw new IncalculablePayloadException('Payload' . ' content length is required and can not be' . ' calculated.');
+                    }
+                    $request = $request->withHeader('content-length', $size);
+                }
+            }
+        }
+        return $nextHandler($command, $request);
+    }
+}