Summary:
- add Response header to the TTY stdout echo path for chat/editor/stdout
- document the Response header behavior in acw CLI and dispatch docs
- assert Response header ordering in the TTY stdout test

Files:
- src/cli/acw/dispatch.sh: emit Response header after the user prompt echo on TTY stdout.
- docs/cli/acw.md: document Response header for TTY stdout chat/editor mode.
- src/cli/acw/dispatch.md: describe Response header in stdout capture behavior.
- tests/cli/test-acw-flags.sh: assert Response header presence and ordering on TTY stdout; ensure non-TTY excludes it.
- tests/cli/test-acw-flags.md: update TTY echo expectations to include Response header.

Issue: #798
Tests: `bash tests/cli/test-acw-flags.sh` (passed)