Natural-language matching (#598):
- Deactivation computed first, word-order tolerant: 'turn caveman mode
off' used to ACTIVATE caveman (and reset the level to default),
'turn caveman off' was a no-op.
- 'enable caveman and stop apologizing' no longer deactivates (the old
stop-guard fired on 'stop' anywhere, then the deactivation regex
matched 'caveman and stop').
- Questions ('what is caveman mode?') no longer arm the mode.
- 'normal mode' deactivates only as a command or with caveman context
('how do I exit vim normal mode' no longer kills the session mode).
- Prompts normalized to one line so multiline input matches.
- Scoped brevity ('be brief in the summary section') is a one-off
instruction, not a session-wide switch.
One-shot modes (#599):
- /caveman-commit|-review|-compress save the displaced prose mode to
.caveman-active.prev and the next ordinary prompt restores it (or
deactivates if caveman wasn't active before) — SKILL.md's 'level
persist until changed or session end' holds again.
- Plugin-namespaced /caveman:caveman-commit and -review recognized
(only compress and stats had the variant).
- Deactivation clears the saved prev so nothing resurrects the mode.
Fixes#598, fixes#599
