Summary

• Add tui.custom_working_messages config, defaulting to true, with TOML parsing in core and ACP config loaders.
• Add a /config toggle that persists the setting and updates the active status indicator.
• Use plain Working status text when custom working messages are disabled, and document the setting.

Test Plan

• cargo test -p codex-core --lib tui_config_custom_working_messages
• cargo test -p nori-acp test_nori_config --lib
• cargo test -p nori-tui custom_working_messages --lib
• cargo clippy -p codex-core -p nori-acp -p nori-tui --lib --all-targets
• cargo build --bin nori
• cargo build -p mock-acp-agent
• cargo test -p tui-pty-e2e
• cargo fmt
• git diff --check