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/PhpHash.php

@@ -0,0 +1,65 @@
+<?php
+
+namespace DeliciousBrains\WP_Offload_Media\Aws3\Aws;
+
+/**
+ * Incremental hashing using PHP's hash functions.
+ */
+class PhpHash implements HashInterface
+{
+    /** @var resource|\HashContext */
+    private $context;
+    /** @var string */
+    private $algo;
+    /** @var array */
+    private $options;
+    /** @var string */
+    private $hash;
+    /**
+     * @param string $algo Hashing algorithm. One of PHP's hash_algos()
+     *     return values (e.g. md5, sha1, etc...).
+     * @param array  $options Associative array of hashing options:
+     *     - key: Secret key used with the hashing algorithm.
+     *     - base64: Set to true to base64 encode the value when complete.
+     */
+    public function __construct($algo, array $options = [])
+    {
+        $this->algo = $algo;
+        $this->options = $options;
+    }
+    public function update($data)
+    {
+        if ($this->hash !== null) {
+            $this->reset();
+        }
+        \hash_update($this->getContext(), $data);
+    }
+    public function complete()
+    {
+        if ($this->hash) {
+            return $this->hash;
+        }
+        $this->hash = \hash_final($this->getContext(), \true);
+        if (isset($this->options['base64']) && $this->options['base64']) {
+            $this->hash = \base64_encode($this->hash);
+        }
+        return $this->hash;
+    }
+    public function reset()
+    {
+        $this->context = $this->hash = null;
+    }
+    /**
+     * Get a hash context or create one if needed
+     *
+     * @return resource|\HashContext 
+     */
+    private function getContext()
+    {
+        if (!$this->context) {
+            $key = isset($this->options['key']) ? $this->options['key'] : '';
+            $this->context = \hash_init($this->algo, $key ? \HASH_HMAC : 0, $key);
+        }
+        return $this->context;
+    }
+}