Rework the dashboard into two looks over one behaviour

A dashboard is a wall panel somebody hangs in their own hallway, so it
now wears what they choose: a look, and a palette of their own colours.

Two complete component sets live under `Dashboard/ui/` — `glass`
(translucent panes over a slowly moving ground) and `material` (Material
3 tonal cards) — behind one prop contract. Every control's state,
keyboard and `aria-` live in `ui/core` and are shared, so the two sets
are the same dashboard drawn twice rather than two products: a set only
decides what a control looks like while doing it.

Four settings join the channel, each drivable by a flow like any other:
`look`, `palette`, `background` and `touch`. A palette is an ordered list
of hex colours — background, surface, primary, accent, text, then more
chart colours — pasted from a coolors.co link or typed, written onto the
canvas as the token variables everything already reads. Trailing roles
are derived, so three colours are a whole dashboard, and derived text is
held to AA rather than trusted (`theme.check.ts` measures it). A palette
also decides light or dark, since its first colour is the ground.

Widgets are measured against their own tile with container queries rather
than against the viewport, animate through `motion`, and can be drawn
without their title. The three reworks:

- a bar draws a row per reading, up to eight, each in the dashboard's own
  data colours and each able to carry its own scale — replacing readings
  nested in one fill, which could only ever share one colour and stop at
  three. Documents written the old way are read as rows.
- a chart's range picker moved to a column down its right-hand edge, which
  gives the plot back a whole row of a short tile.
- the colour wheel became a disc: hue is the angle and saturation the
  distance from the middle, so a colour is one gesture rather than three,
  with brightness on a slider beside it.

`index.css` and `lib/motion.ts` are untouched — the dashboard overrides
token *values* on its canvas, never the blocks the two repos share.

DESIGN.md

@@ -35,3 +35,11 @@ One breakpoint, `md` (768px), and a phone inspects rather than arranges: no
 dragging, no placing, no resizing. The rules that keep it that way — and the
 "nothing scrolls horizontally" check that enforces them — are in
 DESIGN-GUIDELINES.md → Responsive.
+
+## Dashboards
+
+A user-defined dashboard deliberately steps outside the shared design system:
+it has two complete component sets of its own (`glass` and `material`) and
+takes its colours from the document rather than from the tokens. See
+DESIGN-GUIDELINES.md → The dashboard is exempt. The shells, the flow editor and
+every admin screen are unaffected.