app-server: add Unix socket transport (#18255)

## Summary
- add unix:// app-server transport backed by the shared codex-uds crate
- reuse the websocket connection loop for axum and tungstenite-backed
streams
- add codex app-server proxy to bridge stdio clients to the control
socket
- tolerate Windows UDS backends that report a missing rendezvous path as
connection refused before binding

## Tests
- cargo test -p codex-app-server
control_socket_acceptor_forwards_websocket_text_messages_and_pings
- cargo test -p codex-app-server
- just fmt
- just fix -p codex-app-server
- git -c core.fsmonitor=false diff --check

codex-rs/Cargo.lock

@@ -1867,6 +1867,7 @@ dependencies = [
  "codex-state",
  "codex-thread-store",
  "codex-tools",
+ "codex-uds",
  "codex-utils-absolute-path",
  "codex-utils-cargo-bin",
  "codex-utils-cli",