Fix Codex web composer submit timing

[edwin-zvs]

Summary

• delay Codex web composer submit Enter until after Codex's paste-burst suppression window
• keep non-Codex PTY composer submit behavior unchanged
• add web smoke coverage for Codex submit ordering

Testing

• git diff --check
• cargo build
• cargo test -p agentd-e2e --test web_smoke web_client_loads_and_websocket_connects

Notes

• Hot reload is pointed at this worktree's web assets for manual verification.