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/domain-check-response.php

@@ -0,0 +1,43 @@
+<?php
+
+namespace DeliciousBrains\WP_Offload_Media\Pro\Integrations\Assets;
+
+use AS3CF_Utils;
+use DeliciousBrains\WP_Offload_Media\Settings\Exceptions\Signature_Verification_Exception;
+use WP_REST_Response;
+
+class Domain_Check_Response extends WP_REST_Response {
+
+	/**
+	 * Verify that this response is valid for the given hashed signature.
+	 *
+	 * @param string $signature A hashed signature to verify this response against.
+	 *
+	 * @throws Signature_Verification_Exception
+	 */
+	public function verify_signature( string $signature ) {
+		if ( ! wp_check_password( $this->raw_signature(), $signature ) ) {
+			throw new Signature_Verification_Exception(
+				__( 'Invalid request signature.', 'amazon-s3-and-cloudfront' )
+			);
+		}
+	}
+
+	/**
+	 * Get the hashed signature for this response.
+	 *
+	 * @return string
+	 */
+	public function hashed_signature(): string {
+		return wp_hash_password( $this->raw_signature() );
+	}
+
+	/**
+	 * Get the raw signature for this response.
+	 *
+	 * @return string
+	 */
+	protected function raw_signature(): string {
+		return AS3CF_Utils::reduce_url( network_home_url() ) . '|' . json_encode( $this->jsonSerialize() ) . '|' . AUTH_SALT;
+	}
+}