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

classes/api/api-manager.php

@@ -0,0 +1,87 @@
+<?php
+
+namespace DeliciousBrains\WP_Offload_Media\API;
+
+class API_Manager {
+
+	/**
+	 * @var API_Manager
+	 */
+	protected static $instance;
+
+	/**
+	 * @var array
+	 */
+	private $api_endpoints;
+
+	/**
+	 * Protected constructor to prevent creating a new instance of the
+	 * class via the `new` operator from outside this class.
+	 */
+	protected function __construct() {
+		$this->api_endpoints = array();
+	}
+
+	/**
+	 * Make this class a singleton.
+	 *
+	 * Use this instead of __construct().
+	 *
+	 * @return API_Manager
+	 */
+	public static function get_instance(): API_Manager {
+		if ( ! isset( static::$instance ) && ! ( self::$instance instanceof API_Manager ) ) {
+			static::$instance = new API_Manager();
+		}
+
+		return static::$instance;
+	}
+
+	/**
+	 * Get a named API Endpoint handler instance.
+	 *
+	 * @param string $name
+	 *
+	 * @return API|null
+	 */
+	public function get_api_endpoint( string $name ): ?API {
+		if ( ! empty( $name ) && array_key_exists( $name, $this->api_endpoints ) ) {
+			return $this->api_endpoints[ $name ];
+		}
+
+		return null;
+	}
+
+	/**
+	 * Returns a list of APi Endpoint paths keyed by their name.
+	 *
+	 * @return array
+	 */
+	public function api_endpoints(): array {
+		return array_map( function ( API $api_endpoint ) {
+			return $api_endpoint->endpoint();
+		}, $this->api_endpoints );
+	}
+
+	/**
+	 * Register API Endpoint handler instance.
+	 *
+	 * @param string $name
+	 * @param API    $api
+	 */
+	public function register_api_endpoint( string $name, API $api ) {
+		$this->api_endpoints[ $name ] = $api;
+	}
+
+	/**
+	 * As this class is a singleton it should not be clone-able.
+	 */
+	protected function __clone() {
+	}
+
+	/**
+	 * As this class is a singleton it should not be able to be unserialized.
+	 */
+	public function __wakeup() {
+	}
+}