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/RetryMiddleware.php

@@ -0,0 +1,91 @@
+<?php
+
+namespace DeliciousBrains\WP_Offload_Media\Aws3\GuzzleHttp;
+
+use DeliciousBrains\WP_Offload_Media\Aws3\GuzzleHttp\Promise as P;
+use DeliciousBrains\WP_Offload_Media\Aws3\GuzzleHttp\Promise\PromiseInterface;
+use DeliciousBrains\WP_Offload_Media\Aws3\Psr\Http\Message\RequestInterface;
+use DeliciousBrains\WP_Offload_Media\Aws3\Psr\Http\Message\ResponseInterface;
+/**
+ * Middleware that retries requests based on the boolean result of
+ * invoking the provided "decider" function.
+ *
+ * @final
+ */
+class RetryMiddleware
+{
+    /**
+     * @var callable(RequestInterface, array): PromiseInterface
+     */
+    private $nextHandler;
+    /**
+     * @var callable
+     */
+    private $decider;
+    /**
+     * @var callable(int)
+     */
+    private $delay;
+    /**
+     * @param callable                                            $decider     Function that accepts the number of retries,
+     *                                                                         a request, [response], and [exception] and
+     *                                                                         returns true if the request is to be
+     *                                                                         retried.
+     * @param callable(RequestInterface, array): PromiseInterface $nextHandler Next handler to invoke.
+     * @param (callable(int): int)|null                           $delay       Function that accepts the number of retries
+     *                                                                         and returns the number of
+     *                                                                         milliseconds to delay.
+     */
+    public function __construct(callable $decider, callable $nextHandler, ?callable $delay = null)
+    {
+        $this->decider = $decider;
+        $this->nextHandler = $nextHandler;
+        $this->delay = $delay ?: __CLASS__ . '::exponentialDelay';
+    }
+    /**
+     * Default exponential backoff delay function.
+     *
+     * @return int milliseconds.
+     */
+    public static function exponentialDelay(int $retries) : int
+    {
+        return (int) 2 ** ($retries - 1) * 1000;
+    }
+    public function __invoke(RequestInterface $request, array $options) : PromiseInterface
+    {
+        if (!isset($options['retries'])) {
+            $options['retries'] = 0;
+        }
+        $fn = $this->nextHandler;
+        return $fn($request, $options)->then($this->onFulfilled($request, $options), $this->onRejected($request, $options));
+    }
+    /**
+     * Execute fulfilled closure
+     */
+    private function onFulfilled(RequestInterface $request, array $options) : callable
+    {
+        return function ($value) use($request, $options) {
+            if (!($this->decider)($options['retries'], $request, $value, null)) {
+                return $value;
+            }
+            return $this->doRetry($request, $options, $value);
+        };
+    }
+    /**
+     * Execute rejected closure
+     */
+    private function onRejected(RequestInterface $req, array $options) : callable
+    {
+        return function ($reason) use($req, $options) {
+            if (!($this->decider)($options['retries'], $req, null, $reason)) {
+                return P\Create::rejectionFor($reason);
+            }
+            return $this->doRetry($req, $options);
+        };
+    }
+    private function doRetry(RequestInterface $request, array $options, ?ResponseInterface $response = null) : PromiseInterface
+    {
+        $options['delay'] = ($this->delay)(++$options['retries'], $response, $request);
+        return $this($request, $options);
+    }
+}