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/S3/PutObjectUrlMiddleware.php

@@ -0,0 +1,52 @@
+<?php
+
+namespace DeliciousBrains\WP_Offload_Media\Aws3\Aws\S3;
+
+use DeliciousBrains\WP_Offload_Media\Aws3\Aws\CommandInterface;
+use DeliciousBrains\WP_Offload_Media\Aws3\Aws\ResultInterface;
+use DeliciousBrains\WP_Offload_Media\Aws3\Psr\Http\Message\RequestInterface;
+/**
+ * Injects ObjectURL into the result of the PutObject operation.
+ *
+ * @internal
+ */
+class PutObjectUrlMiddleware
+{
+    /** @var callable  */
+    private $nextHandler;
+    /**
+     * Create a middleware wrapper function.
+     *
+     * @return callable
+     */
+    public static function wrap()
+    {
+        return function (callable $handler) {
+            return new self($handler);
+        };
+    }
+    /**
+     * @param callable $nextHandler Next handler to invoke.
+     */
+    public function __construct(callable $nextHandler)
+    {
+        $this->nextHandler = $nextHandler;
+    }
+    public function __invoke(CommandInterface $command, RequestInterface $request = null)
+    {
+        $next = $this->nextHandler;
+        return $next($command, $request)->then(function (ResultInterface $result) use($command) {
+            $name = $command->getName();
+            switch ($name) {
+                case 'PutObject':
+                case 'CopyObject':
+                    $result['ObjectURL'] = isset($result['@metadata']['effectiveUri']) ? $result['@metadata']['effectiveUri'] : null;
+                    break;
+                case 'CompleteMultipartUpload':
+                    $result['ObjectURL'] = \urldecode($result['Location'] ?? '');
+                    break;
+            }
+            return $result;
+        });
+    }
+}