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/pro/background-processes/downloader-process.php

@@ -0,0 +1,109 @@
+<?php
+
+namespace DeliciousBrains\WP_Offload_Media\Pro\Background_Processes;
+
+use DeliciousBrains\WP_Offload_Media\Items\Download_Handler;
+use DeliciousBrains\WP_Offload_Media\Items\Item;
+use Exception;
+
+class Downloader_Process extends Background_Tool_Process {
+
+	/**
+	 * @var string
+	 */
+	protected $action = 'downloader';
+
+	/**
+	 * Process items chunk.
+	 *
+	 * @param string $source_type
+	 * @param array  $source_ids
+	 * @param int    $blog_id
+	 *
+	 * @return array
+	 *
+	 * @throws Exception
+	 */
+	protected function process_items_chunk( $source_type, $source_ids, $blog_id ) {
+		$processed = $source_ids;
+
+		foreach ( $source_ids as $source_id ) {
+			$this->handle_item( $source_type, $source_id, $blog_id );
+		}
+
+		// Whether downloaded to local or not, we processed every item.
+		return $processed;
+	}
+
+	/**
+	 * Download the item from bucket.
+	 *
+	 * @param string $source_type
+	 * @param int    $source_id
+	 * @param int    $blog_id
+	 *
+	 * @return bool
+	 * @throws Exception
+	 */
+	protected function handle_item( $source_type, $source_id, $blog_id ) {
+		/** @var Item $class */
+		$class      = $this->as3cf->get_source_type_class( $source_type );
+		$as3cf_item = $class::get_by_source_id( $source_id );
+
+		if ( ! $as3cf_item ) {
+			return false;
+		}
+
+		/** @var Download_Handler $download_handler */
+		$download_handler = $this->as3cf->get_item_handler( Download_Handler::get_item_handler_key_name() );
+		$result           = $download_handler->handle( $as3cf_item );
+
+		if ( is_wp_error( $result ) ) {
+			foreach ( $result->get_error_messages() as $error_message ) {
+				$error_msg = sprintf( __( 'Error downloading to server - %s', 'amazon-s3-and-cloudfront' ), $error_message );
+				$this->record_error( $blog_id, $source_type, $source_id, $error_msg );
+			}
+
+			return false;
+		}
+
+		return true;
+	}
+
+	/**
+	 * Get complete notice message.
+	 *
+	 * @return string
+	 */
+	protected function get_complete_message() {
+		return __( 'Finished downloading media files to local server.', 'amazon-s3-and-cloudfront' );
+	}
+
+	/**
+	 * Called when background process has been cancelled.
+	 */
+	protected function cancelled() {
+		// Do nothing at the moment.
+	}
+
+	/**
+	 * Called when background process has been paused.
+	 */
+	protected function paused() {
+		// Do nothing at the moment.
+	}
+
+	/**
+	 * Called when background process has been resumed.
+	 */
+	protected function resumed() {
+		// Do nothing at the moment.
+	}
+
+	/**
+	 * Called when background process has completed.
+	 */
+	protected function completed() {
+		// Do nothing at the moment.
+	}
+}