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/Gcp/google/grpc-gcp/src/GCPUnaryCall.php

@@ -0,0 +1,68 @@
+<?php
+
+/*
+ *
+ * Copyright 2018 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+namespace DeliciousBrains\WP_Offload_Media\Gcp\Grpc\Gcp;
+
+/**
+ * Represents an active call that sends a single message and then gets a
+ * single response.
+ */
+class GCPUnaryCall extends GcpBaseCall
+{
+    protected function createRealCall($channel)
+    {
+        $this->real_call = new \DeliciousBrains\WP_Offload_Media\Gcp\Grpc\UnaryCall($channel, $this->method, $this->deserialize, $this->options);
+        $this->has_real_call = \true;
+        return $this->real_call;
+    }
+    /**
+     * Pick a channel and start the call.
+     *
+     * @param mixed $data     The data to send
+     * @param array $metadata Metadata to send with the call, if applicable
+     *                        (optional)
+     * @param array $options  An array of options, possible keys:
+     *                        'flags' => a number (optional)
+     */
+    public function start($argument, $metadata, $options)
+    {
+        $channel_ref = $this->_rpcPreProcess($argument);
+        $real_channel = $channel_ref->getRealChannel($this->gcp_channel->credentials);
+        $this->createRealCall($real_channel);
+        $this->real_call->start($argument, $metadata, $options);
+    }
+    /**
+     * Wait for the server to respond with data and a status.
+     *
+     * @return array [response data, status]
+     */
+    public function wait()
+    {
+        list($response, $status) = $this->real_call->wait();
+        $this->_rpcPostProcess($status, $response);
+        return [$response, $status];
+    }
+    /**
+     * @return mixed The metadata sent by the server
+     */
+    public function getMetadata()
+    {
+        return $this->real_call->getMetadata();
+    }
+}