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/Psr7/PumpStream.php

@@ -0,0 +1,149 @@
+<?php
+
+declare (strict_types=1);
+namespace DeliciousBrains\WP_Offload_Media\Aws3\GuzzleHttp\Psr7;
+
+use DeliciousBrains\WP_Offload_Media\Aws3\Psr\Http\Message\StreamInterface;
+/**
+ * Provides a read only stream that pumps data from a PHP callable.
+ *
+ * When invoking the provided callable, the PumpStream will pass the amount of
+ * data requested to read to the callable. The callable can choose to ignore
+ * this value and return fewer or more bytes than requested. Any extra data
+ * returned by the provided callable is buffered internally until drained using
+ * the read() function of the PumpStream. The provided callable MUST return
+ * false when there is no more data to read.
+ */
+final class PumpStream implements StreamInterface
+{
+    /** @var callable(int): (string|false|null)|null */
+    private $source;
+    /** @var int|null */
+    private $size;
+    /** @var int */
+    private $tellPos = 0;
+    /** @var array */
+    private $metadata;
+    /** @var BufferStream */
+    private $buffer;
+    /**
+     * @param callable(int): (string|false|null)  $source  Source of the stream data. The callable MAY
+     *                                                     accept an integer argument used to control the
+     *                                                     amount of data to return. The callable MUST
+     *                                                     return a string when called, or false|null on error
+     *                                                     or EOF.
+     * @param array{size?: int, metadata?: array} $options Stream options:
+     *                                                     - metadata: Hash of metadata to use with stream.
+     *                                                     - size: Size of the stream, if known.
+     */
+    public function __construct(callable $source, array $options = [])
+    {
+        $this->source = $source;
+        $this->size = $options['size'] ?? null;
+        $this->metadata = $options['metadata'] ?? [];
+        $this->buffer = new BufferStream();
+    }
+    public function __toString() : string
+    {
+        try {
+            return Utils::copyToString($this);
+        } catch (\Throwable $e) {
+            if (\PHP_VERSION_ID >= 70400) {
+                throw $e;
+            }
+            \trigger_error(\sprintf('%s::__toString exception: %s', self::class, (string) $e), \E_USER_ERROR);
+            return '';
+        }
+    }
+    public function close() : void
+    {
+        $this->detach();
+    }
+    public function detach()
+    {
+        $this->tellPos = 0;
+        $this->source = null;
+        return null;
+    }
+    public function getSize() : ?int
+    {
+        return $this->size;
+    }
+    public function tell() : int
+    {
+        return $this->tellPos;
+    }
+    public function eof() : bool
+    {
+        return $this->source === null;
+    }
+    public function isSeekable() : bool
+    {
+        return \false;
+    }
+    public function rewind() : void
+    {
+        $this->seek(0);
+    }
+    public function seek($offset, $whence = \SEEK_SET) : void
+    {
+        throw new \RuntimeException('Cannot seek a PumpStream');
+    }
+    public function isWritable() : bool
+    {
+        return \false;
+    }
+    public function write($string) : int
+    {
+        throw new \RuntimeException('Cannot write to a PumpStream');
+    }
+    public function isReadable() : bool
+    {
+        return \true;
+    }
+    public function read($length) : string
+    {
+        $data = $this->buffer->read($length);
+        $readLen = \strlen($data);
+        $this->tellPos += $readLen;
+        $remaining = $length - $readLen;
+        if ($remaining) {
+            $this->pump($remaining);
+            $data .= $this->buffer->read($remaining);
+            $this->tellPos += \strlen($data) - $readLen;
+        }
+        return $data;
+    }
+    public function getContents() : string
+    {
+        $result = '';
+        while (!$this->eof()) {
+            $result .= $this->read(1000000);
+        }
+        return $result;
+    }
+    /**
+     * @return mixed
+     */
+    public function getMetadata($key = null)
+    {
+        if (!$key) {
+            return $this->metadata;
+        }
+        return $this->metadata[$key] ?? null;
+    }
+    private function pump(int $length) : void
+    {
+        if ($this->source !== null) {
+            do {
+                $data = ($this->source)($length);
+                if ($data === \false || $data === null) {
+                    $this->source = null;
+                    return;
+                }
+                $this->buffer->write($data);
+                $length -= \strlen($data);
+            } while ($length > 0);
+        }
+    }
+}