Move nuncio-tui, nuncio-gui (+src-tauri, ui), and nuncio-mcp out of the Cargo
workspace into _reference/ (git renames; history preserved), retained for the
Phase 5 native client-repo extraction. Remove the unused nuncio-mcp dev-dep
from nunciod and rework daemon_e2e_test to drive the real nuncio-cli
HeadlessRunner (more coverage, no archived-shell dependency). Workspace is now
engine + daemon + reference CLI (8 members); build/clippy/tests green.
Refs #145
