Port Brave Sync server to Rust

Use SQLite for persistence and generate Rust protobuf bindings at build time.

Add Docker image support for containerized deployment.

Co-Authored-By: codex <[email protected]>

schema/protobuf/sync_pb/extension_setting_specifics.proto

@@ -0,0 +1,31 @@
+// Copyright 2012 The Chromium Authors
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+//
+// Sync protocol datatype extension for an extension setting.
+
+// If you change or add any fields in this file, update proto_visitors.h and
+// potentially proto_enum_conversions.{h, cc}.
+
+syntax = "proto2";
+
+option go_package = "./sync_pb";
+
+option java_multiple_files = true;
+option java_package = "org.chromium.components.sync.protocol";
+
+option optimize_for = LITE_RUNTIME;
+
+package sync_pb;
+
+// Properties of extension setting sync objects.
+message ExtensionSettingSpecifics {
+  // Id of the extension the setting is for.
+  optional string extension_id = 1;
+
+  // Setting key.
+  optional string key = 2;
+
+  // Setting value serialized as JSON.
+  optional string value = 3;
+}