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/LazyOpenStream.php

@@ -0,0 +1,41 @@
+<?php
+
+declare (strict_types=1);
+namespace DeliciousBrains\WP_Offload_Media\Aws3\GuzzleHttp\Psr7;
+
+use DeliciousBrains\WP_Offload_Media\Aws3\Psr\Http\Message\StreamInterface;
+/**
+ * Lazily reads or writes to a file that is opened only after an IO operation
+ * take place on the stream.
+ */
+final class LazyOpenStream implements StreamInterface
+{
+    use StreamDecoratorTrait;
+    /** @var string */
+    private $filename;
+    /** @var string */
+    private $mode;
+    /**
+     * @var StreamInterface
+     */
+    private $stream;
+    /**
+     * @param string $filename File to lazily open
+     * @param string $mode     fopen mode to use when opening the stream
+     */
+    public function __construct(string $filename, string $mode)
+    {
+        $this->filename = $filename;
+        $this->mode = $mode;
+        // unsetting the property forces the first access to go through
+        // __get().
+        unset($this->stream);
+    }
+    /**
+     * Creates the underlying stream lazily when required.
+     */
+    protected function createStream() : StreamInterface
+    {
+        return Utils::streamFor(Utils::tryFopen($this->filename, $this->mode));
+    }
+}