docs(faces): where faces live and what the first two steps settled (improvise-nn4s)

context/code/protocol.md gains section 10 and tui.md's colour section now
describes face_style; the pointers to axis_fg, minibuf_fg and AxisColor
elsewhere follow. Evidence for the new tests.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01VdfEGXA7aJ6ftMsCc9PJze

.agents/skills/code-review/SKILL.md

@@ -59,7 +59,8 @@ they mean, rather than testing for the variant
 **Layering.** `forbidden/2` in `kb.pl` is the authority:
 `improvise-core` no UI/IO, `improvise-io` no UI/commands, `improvise-command`
 no ratatui/crossterm. A ratatui type in core is the usual violation — the fix
-is a semantic enum in core that the render layer maps (see `AxisColor`).
+is a semantic value the render layer maps; for appearance that is a `Face` in
+`improvise-protocol`, resolved by `draw.rs::face_style` (ADR 004).
 
 **`Option`/`Result`/`Box` at the boundaries.** Wrap at parse/lookup/IO, unwrap
 early, keep core logic on concrete values. Heap-container plumbing should be