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/integrations/integration.php

@@ -0,0 +1,53 @@
+<?php
+
+namespace DeliciousBrains\WP_Offload_Media\Integrations;
+
+use Amazon_S3_And_CloudFront;
+
+abstract class Integration {
+
+	/**
+	 * @var Amazon_S3_And_CloudFront
+	 */
+	protected $as3cf;
+
+	/**
+	 * Integration constructor.
+	 *
+	 * @param Amazon_S3_And_CloudFront $as3cf
+	 */
+	public function __construct( Amazon_S3_And_CloudFront $as3cf ) {
+		$this->as3cf = $as3cf;
+	}
+
+	/**
+	 * Is installed?
+	 *
+	 * @return bool
+	 */
+	public static function is_installed(): bool {
+		return false;
+	}
+
+	/**
+	 * Is this integration enabled?
+	 *
+	 * While the integration's dependencies may be installed,
+	 * it is possible that the integration is disabled for other reasons.
+	 *
+	 * @return bool
+	 */
+	public function is_enabled(): bool {
+		return static::is_installed();
+	}
+
+	/**
+	 * Init integration.
+	 */
+	abstract public function init();
+
+	/**
+	 * Set up the integration.
+	 */
+	abstract public function setup();
+}