feat!(spawn-docker-jdk): replace OkHttp and junixsocket with pure JDK HTTP

[deer]

Replaces the OkHttp-based Docker client with a zero-third-party-dependency implementation using only standard JDK APIs.

What changed:

• Renamed module spawn-docker-okhttp → spawn-docker-jdk (package build.spawn.docker.jdk)
• Introduced HttpTransport interface decoupling all 22 command classes from any HTTP library
• TCP sessions now use java.net.http.HttpClient (JavaHttpClientTransport)
• Unix domain socket sessions now use java.nio.channels.SocketChannel + UnixDomainSocketAddress (UnixSocketHttpTransport) — no more junixsocket
• Http11Parser handles HTTP/1.1 framing (status line, headers, Content-Length, chunked) over raw socket streams
• Deleted OkHttp-specific dead code: ConnectTimeout, ReadTimeout, WriteTimeout option classes

Dependencies removed:

• com.squareup.okhttp3:okhttp
• org.jetbrains.kotlin:kotlin-stdlib
• com.kohlschutter.junixsocket:junixsocket-common
• com.kohlschutter.junixsocket:junixsocket-native-common

Tests added: Http11ParserTest, JavaHttpClientTransportTest