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

vendor/Aws3/Aws/Crypto/MetadataStrategyInterface.php

@@ -0,0 +1,30 @@
+<?php
+
+namespace DeliciousBrains\WP_Offload_Media\Aws3\Aws\Crypto;
+
+interface MetadataStrategyInterface
+{
+    /**
+     * Places the information in the MetadataEnvelope to the strategy specific
+     * location. Populates the PutObject arguments with any information
+     * necessary for loading.
+     *
+     * @param MetadataEnvelope $envelope Encryption data to save according to
+     *                                   the strategy.
+     * @param array $args Starting arguments for PutObject.
+     *
+     * @return array Updated arguments for PutObject.
+     */
+    public function save(MetadataEnvelope $envelope, array $args);
+    /**
+     * Generates a MetadataEnvelope according to the specific strategy using the
+     * passed arguments.
+     *
+     * @param array $args Arguments from Command and Result that contains
+     *                    S3 Object information, relevant headers, and command
+     *                    configuration.
+     *
+     * @return MetadataEnvelope
+     */
+    public function load(array $args);
+}