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/google/cloud-storage/src/ReadStream.php

@@ -0,0 +1,86 @@
+<?php
+
+/**
+ * Copyright 2017 Google Inc. All Rights Reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+namespace DeliciousBrains\WP_Offload_Media\Gcp\Google\Cloud\Storage;
+
+use DeliciousBrains\WP_Offload_Media\Gcp\GuzzleHttp\Psr7\StreamDecoratorTrait;
+use DeliciousBrains\WP_Offload_Media\Gcp\Psr\Http\Message\StreamInterface;
+/**
+ * A Stream implementation that wraps a GuzzleHttp download stream to
+ * provide `getSize()` from the response headers.
+ */
+class ReadStream implements StreamInterface
+{
+    use StreamDecoratorTrait;
+    private $stream;
+    /**
+     * Create a new ReadStream.
+     *
+     * @param StreamInterface $stream The stream interface to wrap
+     */
+    public function __construct(StreamInterface $stream)
+    {
+        $this->stream = $stream;
+    }
+    /**
+     * Return the full size of the buffer. If the underlying stream does
+     * not report it's size, try to fetch the size from the Content-Length
+     * response header.
+     *
+     * @return int The size of the stream.
+     */
+    public function getSize() : ?int
+    {
+        return $this->stream->getSize() ?: $this->getSizeFromMetadata();
+    }
+    /**
+     * Attempt to fetch the size from the Content-Length response header.
+     * If we cannot, return 0.
+     *
+     * @return int The Size of the stream
+     */
+    private function getSizeFromMetadata() : int
+    {
+        foreach ($this->stream->getMetadata('wrapper_data') as $value) {
+            if (\substr($value, 0, 15) == "Content-Length:") {
+                return (int) \substr($value, 16);
+            }
+        }
+        return 0;
+    }
+    /**
+     * Read bytes from the underlying buffer, retrying until we have read
+     * enough bytes or we cannot read any more. We do this because the
+     * internal C code for filling a buffer does not account for when
+     * we try to read large chunks from a user-land stream that does not
+     * return enough bytes.
+     *
+     * @param  int $length The number of bytes to read.
+     * @return string Read bytes from the underlying stream.
+     */
+    public function read($length) : string
+    {
+        $data = '';
+        do {
+            $moreData = $this->stream->read($length);
+            $data .= $moreData;
+            $readLength = \strlen($moreData);
+            $length -= $readLength;
+        } while ($length > 0 && $readLength > 0);
+        return $data;
+    }
+}