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/integrations/core-pro.php

@@ -0,0 +1,52 @@
+<?php
+
+namespace DeliciousBrains\WP_Offload_Media\Pro\Integrations;
+
+use Amazon_S3_And_CloudFront_Pro;
+use DeliciousBrains\WP_Offload_Media\Integrations\Core;
+use DeliciousBrains\WP_Offload_Media\Items\Download_Handler;
+use DeliciousBrains\WP_Offload_Media\Items\Item;
+use DeliciousBrains\WP_Offload_Media\Pro\Items\Remove_Provider_Handler;
+use WP_Error;
+
+class Core_Pro extends Core {
+	/**
+	 * @var Amazon_S3_And_CloudFront_Pro
+	 */
+	protected $as3cf;
+
+	/**
+	 * @inheritDoc
+	 */
+	public function setup() {
+		parent::setup();
+
+		add_action( 'as3cf_pre_handle_item_' . Remove_Provider_Handler::get_item_handler_key_name(), array( $this, 'maybe_download_files' ), 10, 3 );
+	}
+
+	/**
+	 * Before removing from provider, maybe download files.
+	 *
+	 * @handles as3cf_pre_handle_item_remove-provider
+	 *
+	 * @param bool  $cancel     Should the action on the item be cancelled?
+	 * @param Item  $as3cf_item The item that the action is being handled for.
+	 * @param array $options    Handler dependent options that may have been set for the action.
+	 *
+	 * @return bool|WP_Error
+	 */
+	public function maybe_download_files( $cancel, Item $as3cf_item, array $options ) {
+		if ( false === $cancel && ! empty( $options['verify_exists_on_local'] ) ) {
+			$download_handler = $this->as3cf->get_item_handler( Download_Handler::get_item_handler_key_name() );
+			$result           = $download_handler->handle( $as3cf_item );
+
+			// If there was any kind of error, then remove from provider should not proceed.
+			// Because this is an unexpected error, bubble it.
+			if ( is_wp_error( $result ) ) {
+				return $result;
+			}
+		}
+
+		return $cancel;
+	}
+}