docs(scripts): add --help to remaining scripts; document scripts + layout in README

- Add a -h/--help guard (prints the usage header) to the five scripts
  that lacked one: smoke.sh, smoke-e2e.sh, test-features.sh,
  demo-save-load.sh, sandbox-bootstrap.sh. All 15 hh/scripts/*.sh now
  respond to --help.
- README: new "Scripts" section detailing every script (setup, hosting,
  sandbox provisioning, tests) and noting each takes --help; plus an
  archive note for the film-* recording scripts.
- README: new "Window layout" section documenting live pane resizing
  (F4 fullscreen, click/F5 to select + arrows to resize) and the
  /layout save/load/list/rm/reset presets, with matching keybinding-table
  rows.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

hh/scripts/demo-save-load.sh

@@ -14,6 +14,11 @@
 #   --keep   leave the server, container, image and tmux sessions up afterwards
 set -uo pipefail
 
+# -h/--help: print the usage header above and exit.
+case "${1:-}" in
+  -h|--help|-help) sed -n '2,/^set /{/^set /d;s/^# \{0,1\}//;p}' "$0"; exit 0 ;;
+esac
+
 # ---- config -----------------------------------------------------------------
 REPO="$(cd "$(dirname "${BASH_SOURCE[0]}")/../.." && pwd)"
 # Pick a free TCP port so we never collide with a stale server from another