Polish Show HN README demo flow

[JSRRosenbaum]

Summary

• update the README demo GIF to show the ctx-only status → absorb → daydream → print-daydream flow
• add ctx print-daydream so the DMN ledger can be printed to stdout / Unix pipes
• polish the README demo instructions around the CoreTex-native flow
• prompt during local setup to install missing Python prerequisites when possible

Tests

• uv run ruff check System/tests/test_show_hn_cleanup.py System/cli.py System/cli_somatic.py
• uv run pytest -q System/tests/test_show_hn_cleanup.py System/tests/test_show_hn_demo.py
• bash -n setup.sh

[JSRRosenbaum]

Closing in favor of #21, rebased cleanly on main after #17 was merged.