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/AbstractCryptoClient.php

@@ -0,0 +1,102 @@
+<?php
+
+namespace DeliciousBrains\WP_Offload_Media\Aws3\Aws\Crypto;
+
+use DeliciousBrains\WP_Offload_Media\Aws3\Aws\Crypto\Cipher\CipherMethod;
+use DeliciousBrains\WP_Offload_Media\Aws3\Aws\Crypto\Cipher\Cbc;
+use DeliciousBrains\WP_Offload_Media\Aws3\GuzzleHttp\Psr7\Stream;
+/**
+ * Legacy abstract encryption client. New workflows should use
+ * AbstractCryptoClientV2.
+ *
+ * @deprecated
+ * @internal
+ */
+abstract class AbstractCryptoClient
+{
+    public static $supportedCiphers = ['cbc', 'gcm'];
+    public static $supportedKeyWraps = [KmsMaterialsProvider::WRAP_ALGORITHM_NAME];
+    /**
+     * Returns if the passed cipher name is supported for encryption by the SDK.
+     *
+     * @param string $cipherName The name of a cipher to verify is registered.
+     *
+     * @return bool If the cipher passed is in our supported list.
+     */
+    public static function isSupportedCipher($cipherName)
+    {
+        return \in_array($cipherName, self::$supportedCiphers);
+    }
+    /**
+     * Returns an identifier recognizable by `openssl_*` functions, such as
+     * `aes-256-cbc` or `aes-128-ctr`.
+     *
+     * @param string $cipherName Name of the cipher being used for encrypting
+     *                           or decrypting.
+     * @param int $keySize Size of the encryption key, in bits, that will be
+     *                     used.
+     *
+     * @return string
+     */
+    protected abstract function getCipherOpenSslName($cipherName, $keySize);
+    /**
+     * Constructs a CipherMethod for the given name, initialized with the other
+     * data passed for use in encrypting or decrypting.
+     *
+     * @param string $cipherName Name of the cipher to generate for encrypting.
+     * @param string $iv Base Initialization Vector for the cipher.
+     * @param int $keySize Size of the encryption key, in bits, that will be
+     *                     used.
+     *
+     * @return CipherMethod
+     *
+     * @internal
+     */
+    protected abstract function buildCipherMethod($cipherName, $iv, $keySize);
+    /**
+     * Performs a reverse lookup to get the openssl_* cipher name from the
+     * AESName passed in from the MetadataEnvelope.
+     *
+     * @param $aesName
+     *
+     * @return string
+     *
+     * @internal
+     */
+    protected abstract function getCipherFromAesName($aesName);
+    /**
+     * Dependency to provide an interface for building an encryption stream for
+     * data given cipher details, metadata, and materials to do so.
+     *
+     * @param Stream $plaintext Plain-text data to be encrypted using the
+     *                          materials, algorithm, and data provided.
+     * @param array $cipherOptions Options for use in determining the cipher to
+     *                             be used for encrypting data.
+     * @param MaterialsProvider $provider A provider to supply and encrypt
+     *                                    materials used in encryption.
+     * @param MetadataEnvelope $envelope A storage envelope for encryption
+     *                                   metadata to be added to.
+     *
+     * @return AesStreamInterface
+     *
+     * @internal
+     */
+    public abstract function encrypt(Stream $plaintext, array $cipherOptions, MaterialsProvider $provider, MetadataEnvelope $envelope);
+    /**
+     * Dependency to provide an interface for building a decryption stream for
+     * cipher text given metadata and materials to do so.
+     *
+     * @param string $cipherText Plain-text data to be decrypted using the
+     *                           materials, algorithm, and data provided.
+     * @param MaterialsProviderInterface $provider A provider to supply and encrypt
+     *                                             materials used in encryption.
+     * @param MetadataEnvelope $envelope A storage envelope for encryption
+     *                                   metadata to be read from.
+     * @param array $cipherOptions Additional verification options.
+     *
+     * @return AesStreamInterface
+     *
+     * @internal
+     */
+    public abstract function decrypt($cipherText, MaterialsProviderInterface $provider, MetadataEnvelope $envelope, array $cipherOptions = []);
+}