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/InputValidationMiddleware.php

@@ -0,0 +1,62 @@
+<?php
+
+namespace DeliciousBrains\WP_Offload_Media\Aws3\Aws;
+
+use DeliciousBrains\WP_Offload_Media\Aws3\Aws\Api\Service;
+/**
+ * Validates the required input parameters of commands are non empty
+ *
+ * @internal
+ */
+class InputValidationMiddleware
+{
+    /** @var callable */
+    private $nextHandler;
+    /** @var array */
+    private $mandatoryAttributeList;
+    /** @var Service */
+    private $service;
+    /**
+     * Create a middleware wrapper function.
+     *
+     * @param Service $service
+     * @param array $mandatoryAttributeList
+     * @return callable     */
+    public static function wrap(Service $service, $mandatoryAttributeList)
+    {
+        if (!\is_array($mandatoryAttributeList) || \array_filter($mandatoryAttributeList, 'is_string') !== $mandatoryAttributeList) {
+            throw new \InvalidArgumentException("The mandatory attribute list must be an array of strings");
+        }
+        return function (callable $handler) use($service, $mandatoryAttributeList) {
+            return new self($handler, $service, $mandatoryAttributeList);
+        };
+    }
+    public function __construct(callable $nextHandler, Service $service, $mandatoryAttributeList)
+    {
+        $this->service = $service;
+        $this->nextHandler = $nextHandler;
+        $this->mandatoryAttributeList = $mandatoryAttributeList;
+    }
+    public function __invoke(CommandInterface $cmd)
+    {
+        $nextHandler = $this->nextHandler;
+        $op = $this->service->getOperation($cmd->getName())->toArray();
+        if (!empty($op['input']['shape'])) {
+            $service = $this->service->toArray();
+            if (!empty($input = $service['shapes'][$op['input']['shape']])) {
+                if (!empty($input['required'])) {
+                    foreach ($input['required'] as $key => $member) {
+                        if (\in_array($member, $this->mandatoryAttributeList)) {
+                            $argument = \is_string($cmd[$member]) ? \trim($cmd[$member]) : $cmd[$member];
+                            if ($argument === '' || $argument === null) {
+                                $commandName = $cmd->getName();
+                                throw new \InvalidArgumentException("The {$commandName} operation requires non-empty parameter: {$member}");
+                            }
+                        }
+                    }
+                }
+            }
+        }
+        return $nextHandler($cmd);
+    }
+}