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/smoke.sh

@@ -6,6 +6,11 @@
 # Run from anywhere:  hh/scripts/smoke.sh
 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}' "$0"; exit 0 ;;
+esac
+
 HERE="$(cd "$(dirname "$0")/.." && pwd)"   # .../hh
 ROOT="$(cd "$HERE/.." && pwd)"          # repo root
 PY="$ROOT/.venv/bin/python"