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/InstructionFileMetadataStrategy.php

@@ -0,0 +1,73 @@
+<?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;
+use DeliciousBrains\WP_Offload_Media\Aws3\Aws\S3\S3Client;
+/**
+ * Stores and reads encryption MetadataEnvelope information in a file on Amazon
+ * S3.
+ *
+ * A file with the contents of a MetadataEnvelope will be created or read from
+ * alongside the base file on Amazon S3. The provided client will be used for
+ * reading or writing this object. A specified suffix (default of '.instruction'
+ * will be applied to each of the operations involved with the instruction file.
+ *
+ * If there is a failure after an instruction file has been uploaded, it will
+ * not be automatically deleted.
+ */
+class InstructionFileMetadataStrategy implements MetadataStrategyInterface
+{
+    const DEFAULT_FILE_SUFFIX = '.instruction';
+    private $client;
+    private $suffix;
+    /**
+     * @param S3Client $client Client for use in uploading the instruction file.
+     * @param string|null $suffix Optional override suffix for instruction file
+     *                            object keys.
+     */
+    public function __construct(S3Client $client, $suffix = null)
+    {
+        $this->suffix = empty($suffix) ? self::DEFAULT_FILE_SUFFIX : $suffix;
+        $this->client = $client;
+    }
+    /**
+     * Places the information in the MetadataEnvelope to a location on S3.
+     *
+     * @param MetadataEnvelope $envelope Encryption data to save according to
+     *                                   the strategy.
+     * @param array $args Starting arguments for PutObject, used for saving
+     *                    extra the instruction file.
+     *
+     * @return array Updated arguments for PutObject.
+     */
+    public function save(MetadataEnvelope $envelope, array $args)
+    {
+        $this->client->putObject(['Bucket' => $args['Bucket'], 'Key' => $args['Key'] . $this->suffix, 'Body' => \json_encode($envelope)]);
+        return $args;
+    }
+    /**
+     * Uses the strategy's client to retrieve the instruction file from S3 and generates
+     * a MetadataEnvelope from its contents.
+     *
+     * @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)
+    {
+        $result = $this->client->getObject(['Bucket' => $args['Bucket'], 'Key' => $args['Key'] . $this->suffix]);
+        $metadataHeaders = \json_decode($result['Body'], \true);
+        $envelope = new MetadataEnvelope();
+        $constantValues = MetadataEnvelope::getConstantValues();
+        foreach ($constantValues as $constant) {
+            if (!empty($metadataHeaders[$constant])) {
+                $envelope[$constant] = $metadataHeaders[$constant];
+            }
+        }
+        return $envelope;
+    }
+}