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/Cipher/CipherMethod.php

@@ -0,0 +1,55 @@
+<?php
+
+namespace DeliciousBrains\WP_Offload_Media\Aws3\Aws\Crypto\Cipher;
+
+interface CipherMethod
+{
+    /**
+     * Returns an identifier recognizable by `openssl_*` functions, such as
+     * `aes-256-cbc` or `aes-128-ctr`.
+     *
+     * @return string
+     */
+    public function getOpenSslName();
+    /**
+     * Returns an AES recognizable name, such as 'AES/GCM/NoPadding'.
+     *
+     * @return string
+     */
+    public function getAesName();
+    /**
+     * Returns the IV that should be used to initialize the next block in
+     * encrypt or decrypt.
+     *
+     * @return string
+     */
+    public function getCurrentIv();
+    /**
+     * Indicates whether the cipher method used with this IV requires padding
+     * the final block to make sure the plaintext is evenly divisible by the
+     * block size.
+     *
+     * @return boolean
+     */
+    public function requiresPadding();
+    /**
+     * Adjust the return of this::getCurrentIv to reflect a seek performed on
+     * the encryption stream using this IV object.
+     *
+     * @param int $offset
+     * @param int $whence
+     *
+     * @throws LogicException   Thrown if the requested seek is not supported by
+     *                          this IV implementation. For example, a CBC IV
+     *                          only supports a full rewind ($offset === 0 &&
+     *                          $whence === SEEK_SET)
+     */
+    public function seek($offset, $whence = \SEEK_SET);
+    /**
+     * Take account of the last cipher text block to adjust the return of
+     * this::getCurrentIv
+     *
+     * @param string $cipherTextBlock
+     */
+    public function update($cipherTextBlock);
+}