docs: keep the timeline face's design history, not its engineHEADmain

Six prototypes from the world-face work, kept as the record of how the design got to where it is. The first five are self-contained; prototype 6 and the option-A pages load the engine, so they read here but do not run here.

The engine stays out on purpose. It carries the list of places I travel to, with coordinates, and this repo is published — a design record is not worth publishing that for. The README says how to copy the modules in locally to run prototype 6, and gitignore keeps such a copy from being committed by accident.

Dropping the prototype test target with it: the engine and its tests now live in one place, so the suite runs once rather than twice over identical files.

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+# Prototypes
+
+Frozen design history. Every file here is a snapshot of what a design looked
+like on the date in its name, kept so the evolution is walkable. Nothing here
+is maintained, and nothing here is loaded by anything that runs.
+
+Most pages are self-contained: open one and it renders.
+
+## The world face
+
+The world wallpaper's engine used to live here and was hand-copied into
+`~/.dotfiles/settings/faces/` on every change. Both copies were byte-identical
+and both test suites ran the same tests, so the duplication bought nothing and
+risked drift — the two pages' palettes had already diverged enough to break a
+scripted edit.
+
+The live engine, its tests and the lab page now live only with the shipped
+face, in the dotfiles `settings/faces/` directory:
+
+- `timeline-face-engine.js`, `timeline-face-spine.js` — the engine
+- `world.html` — the projected wallpaper
+- `lab.html` — the same engine with a movable home and a fast clock, for
+  trying an idea without touching the wallpaper
+
+`make test-faces` in dotfiles runs their tests.
+
+`2026-07-31-timeline-face-prototype-6.html` and the option-A pages load the
+engine, so they are readable here but not runnable here. The engine is
+deliberately **not** kept in this repo: it carries a list of the places I
+travel to, with coordinates, and this repo is published. A design record is
+not worth publishing that.
+
+To run prototype 6, copy the two engine modules in beside it:
+
+```sh
+cp ~/.dotfiles/settings/faces/timeline-face-*.js docs/prototypes/
+```
+
+They are gitignored here, so a copy stays local. Note that the live engine
+keeps moving: prototype 6 is a photograph of one day's design and a current
+engine may not render it the way it looked.