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/Auth/AuthSelectionMiddleware.php

@@ -0,0 +1,78 @@
+<?php
+
+namespace DeliciousBrains\WP_Offload_Media\Aws3\Aws\Auth;
+
+use DeliciousBrains\WP_Offload_Media\Aws3\Aws\Api\Service;
+use DeliciousBrains\WP_Offload_Media\Aws3\Aws\CommandInterface;
+use Closure;
+use DeliciousBrains\WP_Offload_Media\Aws3\GuzzleHttp\Promise\Promise;
+/**
+ * Handles auth scheme resolution. If a service models and auth scheme using
+ * the `auth` trait and the operation or metadata levels, this middleware will
+ * attempt to select the first compatible auth scheme it encounters and apply its
+ * signature version to the command's `@context` property bag.
+ *
+ * IMPORTANT: this middleware must be added to the "build" step.
+ *
+ * @internal
+ */
+class AuthSelectionMiddleware
+{
+    /** @var callable */
+    private $nextHandler;
+    /** @var AuthSchemeResolverInterface */
+    private $authResolver;
+    /** @var Service */
+    private $api;
+    /**
+     * Create a middleware wrapper function
+     *
+     * @param AuthSchemeResolverInterface $authResolver
+     * @param Service $api
+     * @return Closure
+     */
+    public static function wrap(AuthSchemeResolverInterface $authResolver, Service $api) : Closure
+    {
+        return function (callable $handler) use($authResolver, $api) {
+            return new self($handler, $authResolver, $api);
+        };
+    }
+    /**
+     * @param callable $nextHandler
+     * @param $authResolver
+     * @param callable $identityProvider
+     * @param Service $api
+     */
+    public function __construct(callable $nextHandler, AuthSchemeResolverInterface $authResolver, Service $api)
+    {
+        $this->nextHandler = $nextHandler;
+        $this->authResolver = $authResolver;
+        $this->api = $api;
+    }
+    /**
+     * @param CommandInterface $command
+     *
+     * @return Promise
+     */
+    public function __invoke(CommandInterface $command)
+    {
+        $nextHandler = $this->nextHandler;
+        $serviceAuth = $this->api->getMetadata('auth') ?: [];
+        $operation = $this->api->getOperation($command->getName());
+        $operationAuth = $operation['auth'] ?? [];
+        $unsignedPayload = $operation['unsignedpayload'] ?? \false;
+        $resolvableAuth = $operationAuth ?: $serviceAuth;
+        if (!empty($resolvableAuth)) {
+            if (isset($command['@context']['auth_scheme_resolver']) && $command['@context']['auth_scheme_resolver'] instanceof AuthSchemeResolverInterface) {
+                $resolver = $command['@context']['auth_scheme_resolver'];
+            } else {
+                $resolver = $this->authResolver;
+            }
+            $selectedAuthScheme = $resolver->selectAuthScheme($resolvableAuth, ['unsigned_payload' => $unsignedPayload]);
+            if (!empty($selectedAuthScheme)) {
+                $command['@context']['signature_version'] = $selectedAuthScheme;
+            }
+        }
+        return $nextHandler($command);
+    }
+}