Compile websocket-only exports out of codex-api on wasm and stop enabling Tokio net there by default. Also cut the Tokio process dependency out of wasm builds of codex-git-utils by gating the async git-info module, move codex-utils-image's Tokio dependency to tests, and enable uuid's js RNG feature for wasm in codex-protocol. Native cargo checks passed for codex-api, codex-git-utils, and codex-protocol after the refactor.
## Summary
- add realtime websocket client transport in codex-api
- send session.create on connect with backend prompt and optional
conversation_id
- keep session.update for prompt changes after connect
- switch inbound event parsing to a tagged enum (typed variants instead
of optional field bag)
- add a websocket e2e integration test in
codex-rs/codex-api/tests/realtime_websocket_e2e.rs
## Why
This moves the realtime transport to an explicit session-create
handshake and improves protocol safety with typed inbound events.
## Testing
- Added e2e integration test coverage for session create + event flow in
the API crate.
