Add reflex demo agent: the real hook engine against a simulated agent

[rustfuture]

reflex demo agent walks through six steps of a simulated coding agent and prints Reflex Control's decision for each: an ordinary edit (allow), a write to .env and a shell write into secrets/ (block), git push --force (ask), failing tests at the end of the turn (sent back) and passing tests (allow).

• Every verdict comes from the real engine (check_paths, check_command_in_dir, decide_turn_end with the default config); only the agent's actions and the test results are simulated, and the demo says so on its last line.
• Styled with console (already in the lockfile via cliclack): colored badges, a header box, one-line reasons, a colored summary. Plain words with NO_COLOR; no pauses when REFLEX_DEMO_FAST is set or stdout is not a terminal.
• Unit test pins the six verdict kinds. The README recording (docs/demo/agent.tape, VHS) and the Quick start now use this demo; the old runtime-gate recording is removed.