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/Credentials/AssumeRoleCredentialProvider.php

@@ -0,0 +1,53 @@
+<?php
+
+namespace DeliciousBrains\WP_Offload_Media\Aws3\Aws\Credentials;
+
+use DeliciousBrains\WP_Offload_Media\Aws3\Aws\Exception\CredentialsException;
+use DeliciousBrains\WP_Offload_Media\Aws3\Aws\Result;
+use DeliciousBrains\WP_Offload_Media\Aws3\Aws\Sts\StsClient;
+use DeliciousBrains\WP_Offload_Media\Aws3\GuzzleHttp\Promise\PromiseInterface;
+/**
+ * Credential provider that provides credentials via assuming a role
+ * More Information, see: http://docs.aws.amazon.com/aws-sdk-php/v3/api/api-sts-2011-06-15.html#assumerole
+ */
+class AssumeRoleCredentialProvider
+{
+    const ERROR_MSG = "Missing required 'AssumeRoleCredentialProvider' configuration option: ";
+    /** @var StsClient */
+    private $client;
+    /** @var array */
+    private $assumeRoleParams;
+    /**
+     * The constructor requires following configure parameters:
+     *  - client: a StsClient
+     *  - assume_role_params: Parameters used to make assumeRole call
+     *
+     * @param array $config Configuration options
+     * @throws \InvalidArgumentException
+     */
+    public function __construct(array $config = [])
+    {
+        if (!isset($config['assume_role_params'])) {
+            throw new \InvalidArgumentException(self::ERROR_MSG . "'assume_role_params'.");
+        }
+        if (!isset($config['client'])) {
+            throw new \InvalidArgumentException(self::ERROR_MSG . "'client'.");
+        }
+        $this->client = $config['client'];
+        $this->assumeRoleParams = $config['assume_role_params'];
+    }
+    /**
+     * Loads assume role credentials.
+     *
+     * @return PromiseInterface
+     */
+    public function __invoke()
+    {
+        $client = $this->client;
+        return $client->assumeRoleAsync($this->assumeRoleParams)->then(function (Result $result) {
+            return $this->client->createCredentials($result);
+        })->otherwise(function (\RuntimeException $exception) {
+            throw new CredentialsException("Error in retrieving assume role credentials.", 0, $exception);
+        });
+    }
+}