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

assets/js/pro/installer.js

@@ -0,0 +1,91 @@
+(function( $, wp, _ ) {
+
+	/**
+	 * Create and display a spinner next to an element
+	 *
+	 * @param element
+	 */
+	function createSpinner( element ) {
+		var $spinner = $( '<span />', { class: 'spinner' } );
+		$spinner.css( { 'display': 'inline-block', 'float': 'none', 'visibility': 'visible' } );
+		$spinner.insertAfter( element );
+
+		return $spinner;
+	}
+
+	$( document ).ready( function() {
+
+		// Move the filesystem credential form below the last error notice
+		var $lastNotice = $( '.as3cf-pro-installer-notice' ).last();
+		$( '.as3cfpro-installer-filesystem-creds' ).insertAfter( $lastNotice );
+
+		$( '.as3cfpro-installer-filesystem-creds form' ).on( 'submit', function( e ) {
+			var $submitBtn = $( '#upgrade' );
+			if ( $submitBtn.hasClass( 'button-disabled' ) ) {
+				return;
+			}
+
+			$submitBtn.addClass( 'button-disabled' );
+			$submitBtn.val( as3cfpro_installer.strings.installing + '...' );
+
+			createSpinner( $submitBtn );
+		} );
+
+		$( 'body' ).on( 'click', '.as3cf-pro-installer .install-plugins', function( e ) {
+			e.preventDefault();
+			if ( $( this ).hasClass( 'button-disabled' ) ) {
+				return;
+			}
+
+			$( this ).addClass( 'button-disabled' );
+			$( this ).text( as3cfpro_installer.strings.installing + '...' );
+
+			var $spinner = createSpinner( this );
+
+			/**
+			 * Render an error notice and remove the installer notice
+			 *
+			 * @param string errorMessage
+			 */
+			function installerError( errorMessage ) {
+				var noticeText = as3cfpro_installer.strings.error_installing + ': ' + errorMessage;
+				var noticeHtml = '<div class="error"><p>' + noticeText + '</p></div>';
+
+				$( '.as3cf-pro-installer' ).after( noticeHtml );
+				$( '.as3cf-pro-installer' ).remove();
+
+				$spinner.hide();
+			}
+
+			var process = $( this ).data( 'process' );
+
+			$.ajax( {
+				url: ajaxurl,
+				type: 'POST',
+				dataType: 'json',
+				cache: false,
+				data: {
+					action: 'as3cfpro_install_plugins_' + process,
+					nonce: as3cfpro_installer.nonces.install_plugins
+				},
+				error: function( jqXHR, textStatus, errorThrown ) {
+					installerError( errorThrown + ' - ' + textStatus );
+				},
+				success: function( response ) {
+					if ( _.isObject( response ) && ! _.isUndefined( response.success ) ) {
+
+						if ( response.success ) {
+							window.location.href = response.data.redirect;
+						}
+
+						if ( ! _.isUndefined( response.data.error ) ) {
+							installerError( response.data.error );
+						}
+					}
+				}
+			} );
+		} );
+
+	} );
+
+})( jQuery, wp, _ );