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/Promise/RejectedPromise.php

@@ -0,0 +1,78 @@
+<?php
+
+declare (strict_types=1);
+namespace DeliciousBrains\WP_Offload_Media\Aws3\GuzzleHttp\Promise;
+
+/**
+ * A promise that has been rejected.
+ *
+ * Thenning off of this promise will invoke the onRejected callback
+ * immediately and ignore other callbacks.
+ *
+ * @final
+ */
+class RejectedPromise implements PromiseInterface
+{
+    private $reason;
+    /**
+     * @param mixed $reason
+     */
+    public function __construct($reason)
+    {
+        if (\is_object($reason) && \method_exists($reason, 'then')) {
+            throw new \InvalidArgumentException('You cannot create a RejectedPromise with a promise.');
+        }
+        $this->reason = $reason;
+    }
+    public function then(?callable $onFulfilled = null, ?callable $onRejected = null) : PromiseInterface
+    {
+        // If there's no onRejected callback then just return self.
+        if (!$onRejected) {
+            return $this;
+        }
+        $queue = Utils::queue();
+        $reason = $this->reason;
+        $p = new Promise([$queue, 'run']);
+        $queue->add(static function () use($p, $reason, $onRejected) : void {
+            if (Is::pending($p)) {
+                try {
+                    // Return a resolved promise if onRejected does not throw.
+                    $p->resolve($onRejected($reason));
+                } catch (\Throwable $e) {
+                    // onRejected threw, so return a rejected promise.
+                    $p->reject($e);
+                }
+            }
+        });
+        return $p;
+    }
+    public function otherwise(callable $onRejected) : PromiseInterface
+    {
+        return $this->then(null, $onRejected);
+    }
+    public function wait(bool $unwrap = \true)
+    {
+        if ($unwrap) {
+            throw Create::exceptionFor($this->reason);
+        }
+        return null;
+    }
+    public function getState() : string
+    {
+        return self::REJECTED;
+    }
+    public function resolve($value) : void
+    {
+        throw new \LogicException('Cannot resolve a rejected promise');
+    }
+    public function reject($reason) : void
+    {
+        if ($reason !== $this->reason) {
+            throw new \LogicException('Cannot reject a rejected promise');
+        }
+    }
+    public function cancel() : void
+    {
+        // pass
+    }
+}