Добавление Ktor и выбор движков платформы

Ktor Client is a multiplatform HTTP library, so you write networking once in commonMain and it runs on Android and iOS alike.

Ktor splits into a shared core and per-platform engines. The core gives the API, the engine does the actual socket work.

In your shared module you add ktor-client-core to commonMain so every target can build requests with the same API.

For Android you pick the OkHttp engine, a battle-tested JVM client that Ktor wraps cleanly behind its shared API.

For iOS you pick the Darwin engine, which runs on Apple's native URLSession under the hood for true platform networking.

Each engine belongs in its own source set: OkHttp in androidMain and Darwin in iosMain, never in commonMain.

In commonMain you create an HttpClient with no engine argument, and Ktor auto-selects the one bundled for that platform.

Because only one engine ships per target, Ktor's auto-selection finds it. Your shared code stays free of any platform import.

You can also pass an engine explicitly, which is handy when you want per-platform config like timeouts or proxies.

The client holds real resources, so call close when you no longer need it to release connections cleanly.

This core-plus-engine design lets Ktor reuse each OS's best networking stack while you keep one shared API for all of them.

Ktor shares a core API but needs an engine per platform: OkHttp for Android, Darwin for iOS. Auto-selection keeps shared code clean.