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/assets/api/v1/assets-domain-check.php

@@ -0,0 +1,59 @@
+<?php
+
+namespace DeliciousBrains\WP_Offload_Media\Pro\Integrations\Assets\API\V1;
+
+use DeliciousBrains\WP_Offload_Media\Pro\API\API;
+use DeliciousBrains\WP_Offload_Media\Pro\Integrations\Assets\Domain_Check_Response;
+use WP_REST_Request;
+use WP_REST_Response;
+
+class Assets_Domain_Check extends API {
+	/** @var int */
+	protected static $version = 1;
+
+	/** @var string */
+	protected static $name = 'assets-domain-check';
+
+	/**
+	 * Register REST API routes.
+	 */
+	public function register_routes() {
+		register_rest_route(
+			static::api_namespace(),
+			static::route() . '(?P<key>[\w\d=]+)',
+			array(
+				'methods'             => 'GET',
+				'callback'            => array( $this, 'get_domain_check' ),
+				'permission_callback' => '__return_true', // public access
+			)
+		);
+	}
+
+	/**
+	 * Respond to a GET request to the domain check route, with the given key.
+	 *
+	 * @param WP_REST_Request $request
+	 *
+	 * @return WP_REST_Response
+	 */
+	public function get_domain_check( WP_REST_Request $request ): WP_REST_Response {
+		$response = new Domain_Check_Response( array(
+			'key' => $request->get_param( 'key' ),
+			'ver' => filter_input( INPUT_GET, 'ver' ), // must come in as url param
+		) );
+		$response->header( 'X-As3cf-Signature', $response->hashed_signature() );
+
+		return $this->rest_ensure_response( 'get', static::name(), $response );
+	}
+
+	/**
+	 * Get a URL to the domain check route, with the given key.
+	 *
+	 * @param string $key
+	 *
+	 * @return string
+	 */
+	public function get_url( string $key ): string {
+		return rest_url( static::endpoint() . $key );
+	}
+}

classes/pro/integrations/assets/api/v1/assets-settings.php

@@ -0,0 +1,76 @@
+<?php
+
+namespace DeliciousBrains\WP_Offload_Media\Pro\Integrations\Assets\API\V1;
+
+use DeliciousBrains\WP_Offload_Media\API\V1\Settings;
+use DeliciousBrains\WP_Offload_Media\Pro\Integrations\Assets\Assets;
+
+class Assets_Settings extends Settings {
+	/** @var int */
+	protected static $version = 1;
+
+	/** @var string */
+	protected static $name = 'assets-settings';
+
+	/**
+	 * Common response values for this API endpoint.
+	 *
+	 * @return array
+	 */
+	public function common_response(): array {
+		/** @var Assets|null */
+		$assets = $this->as3cf->get_integration_manager()->get_integration( 'assets' );
+
+		return array(
+			'assets_settings'         => $assets->obfuscate_sensitive_settings( $assets->get_all_settings() ),
+			'assets_defined_settings' => array_keys( $assets->get_defined_settings() ),
+		);
+	}
+
+	/**
+	 * Handle saving settings submitted by user.
+	 *
+	 * @param array $new_settings
+	 *
+	 * @return array
+	 */
+	protected function save_settings( array $new_settings ): array {
+		$changed_keys = array();
+
+		do_action( 'as3cf_pre_save_assets_settings' );
+
+		/** @var Assets $assets */
+		$assets = $this->as3cf->get_integration_manager()->get_integration( 'assets' );
+
+		$allowed      = $assets->get_allowed_settings_keys();
+		$old_settings = $assets->get_all_settings( false );
+
+		// Merge in defined settings as they take precedence and must overwrite anything supplied.
+		// Only needed to allow for validation, during save defined settings are removed from array anyway.
+		$new_settings = array_merge( $new_settings, $assets->get_defined_settings() );
+
+		foreach ( $allowed as $key ) {
+			// Whether defined or not, get rid of old database setting for key.
+			$assets->remove_setting( $key );
+
+			if ( ! isset( $new_settings[ $key ] ) ) {
+				continue;
+			}
+
+			$value = $assets->sanitize_setting( $key, $new_settings[ $key ] );
+
+			$assets->set_setting( $key, $value );
+
+			if ( $this->setting_changed( $old_settings, $key, $value ) ) {
+				$changed_keys[] = $key;
+			}
+		}
+
+		// Great success ...
+		$assets->save_settings();
+
+		do_action( 'as3cf_post_save_assets_settings', true );
+
+		return $changed_keys;
+	}
+}