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/S3/Crypto/HeadersMetadataStrategy.php

@@ -0,0 +1,48 @@
+<?php
+
+namespace DeliciousBrains\WP_Offload_Media\Aws3\Aws\S3\Crypto;
+
+use DeliciousBrains\WP_Offload_Media\Aws3\Aws\Crypto\MetadataStrategyInterface;
+use DeliciousBrains\WP_Offload_Media\Aws3\Aws\Crypto\MetadataEnvelope;
+class HeadersMetadataStrategy implements MetadataStrategyInterface
+{
+    /**
+     * Places the information in the MetadataEnvelope in to the metadata for
+     * the PutObject request of the encrypted object.
+     *
+     * @param MetadataEnvelope $envelope Encryption data to save according to
+     *                                   the strategy.
+     * @param array $args Arguments for PutObject that can be manipulated to
+     *                    store strategy related information.
+     *
+     * @return array Updated arguments for PutObject.
+     */
+    public function save(MetadataEnvelope $envelope, array $args)
+    {
+        foreach ($envelope as $header => $value) {
+            $args['Metadata'][$header] = $value;
+        }
+        return $args;
+    }
+    /**
+     * Generates a MetadataEnvelope according to the metadata headers from the
+     * GetObject result.
+     *
+     * @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)
+    {
+        $envelope = new MetadataEnvelope();
+        $constantValues = MetadataEnvelope::getConstantValues();
+        foreach ($constantValues as $constant) {
+            if (!empty($args['Metadata'][$constant])) {
+                $envelope[$constant] = $args['Metadata'][$constant];
+            }
+        }
+        return $envelope;
+    }
+}