Add `--demo` (and the RDBMS_PLAYGROUND_DEMO env fallback) to enter
demonstration mode, threaded onto App.demo_mode through run_loop —
mirrors the --no-undo plumbing. Off by default, zero footprint when
off. The --help line advertises only the visible keystroke badges;
the Ctrl+] caption trigger is kept low-profile (ADR-0047 D6 updated).
Phase A of ADR-0047; behaviour (badges/captions) lands in B and C.
claude@clouddev1
f879d54721