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/Gcp/ralouphie/getallheaders/src/getallheaders.php

@@ -0,0 +1,38 @@
+<?php
+
+namespace DeliciousBrains\WP_Offload_Media\Gcp;
+
+if (!\function_exists('getallheaders')) {
+    /**
+     * Get all HTTP header key/values as an associative array for the current request.
+     *
+     * @return string[string] The HTTP header key/value pairs.
+     */
+    function getallheaders()
+    {
+        $headers = array();
+        $copy_server = array('CONTENT_TYPE' => 'Content-Type', 'CONTENT_LENGTH' => 'Content-Length', 'CONTENT_MD5' => 'Content-Md5');
+        foreach ($_SERVER as $key => $value) {
+            if (\substr($key, 0, 5) === 'HTTP_') {
+                $key = \substr($key, 5);
+                if (!isset($copy_server[$key]) || !isset($_SERVER[$key])) {
+                    $key = \str_replace(' ', '-', \ucwords(\strtolower(\str_replace('_', ' ', $key))));
+                    $headers[$key] = $value;
+                }
+            } elseif (isset($copy_server[$key])) {
+                $headers[$copy_server[$key]] = $value;
+            }
+        }
+        if (!isset($headers['Authorization'])) {
+            if (isset($_SERVER['REDIRECT_HTTP_AUTHORIZATION'])) {
+                $headers['Authorization'] = $_SERVER['REDIRECT_HTTP_AUTHORIZATION'];
+            } elseif (isset($_SERVER['PHP_AUTH_USER'])) {
+                $basic_pass = isset($_SERVER['PHP_AUTH_PW']) ? $_SERVER['PHP_AUTH_PW'] : '';
+                $headers['Authorization'] = 'Basic ' . \base64_encode($_SERVER['PHP_AUTH_USER'] . ':' . $basic_pass);
+            } elseif (isset($_SERVER['PHP_AUTH_DIGEST'])) {
+                $headers['Authorization'] = $_SERVER['PHP_AUTH_DIGEST'];
+            }
+        }
+        return $headers;
+    }
+}