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/MetadataEnvelope.php

@@ -0,0 +1,53 @@
+<?php
+
+namespace DeliciousBrains\WP_Offload_Media\Aws3\Aws\Crypto;
+
+use DeliciousBrains\WP_Offload_Media\Aws3\Aws\HasDataTrait;
+use ArrayAccess;
+use IteratorAggregate;
+use InvalidArgumentException;
+use JsonSerializable;
+/**
+ * Stores encryption metadata for reading and writing.
+ *
+ * @internal
+ */
+class MetadataEnvelope implements ArrayAccess, IteratorAggregate, JsonSerializable
+{
+    use HasDataTrait;
+    const CONTENT_KEY_V2_HEADER = 'x-amz-key-v2';
+    const IV_HEADER = 'x-amz-iv';
+    const MATERIALS_DESCRIPTION_HEADER = 'x-amz-matdesc';
+    const KEY_WRAP_ALGORITHM_HEADER = 'x-amz-wrap-alg';
+    const CONTENT_CRYPTO_SCHEME_HEADER = 'x-amz-cek-alg';
+    const CRYPTO_TAG_LENGTH_HEADER = 'x-amz-tag-len';
+    const UNENCRYPTED_CONTENT_LENGTH_HEADER = 'x-amz-unencrypted-content-length';
+    private static $constants = [];
+    public static function getConstantValues()
+    {
+        if (empty(self::$constants)) {
+            $reflection = new \ReflectionClass(static::class);
+            foreach (\array_values($reflection->getConstants()) as $constant) {
+                self::$constants[$constant] = \true;
+            }
+        }
+        return \array_keys(self::$constants);
+    }
+    /**
+     * @return void
+     */
+    #[\ReturnTypeWillChange]
+    public function offsetSet($name, $value)
+    {
+        $constants = self::getConstantValues();
+        if (\is_null($name) || !\in_array($name, $constants)) {
+            throw new InvalidArgumentException('MetadataEnvelope fields must' . ' must match a predefined offset; use the header constants.');
+        }
+        $this->data[$name] = $value;
+    }
+    #[\ReturnTypeWillChange]
+    public function jsonSerialize()
+    {
+        return $this->data;
+    }
+}