Add the Fluksio look, and make it the one a dashboard starts in

Two looks were somebody else's language spoken well, and neither was the
product's. A dashboard nobody has dressed yet should look like the rest
of the app, so there is now a third set that follows the root
DESIGN-GUIDELINES.md to the letter — `--card` surfaces told from the page
by a hairline and a low shadow rather than by colour, every control a
pill, 16px panels, frosted floating chrome, one slate-blue accent spent
on what a person can act on — and it is what `look` means when nothing
says otherwise.

That also turns the exemption the other way round. The dashboard is still
allowed to look unlike the product; it just no longer does so by default.
An existing dashboard, which has never named a look, lands on the design
it had before any of this.

Restraint is the style rather than an omission here: no ripple, no glow,
no lift, and a press answered by the colour changing. The one deliberate
departure is the selector, which holds its choice in `--primary` rather
than the `--accent` the segmented rule asks for — that is a decision
about the widget, not about the look, and a control must not change what
it signals when the drawing changes. All three sets hold it the same way.

docs/interface/dashboards.md

@@ -100,7 +100,7 @@ set them.
 
 | Setting | Is | Driven by |
 |---|---|---|
-| **Look** | `Material` or `Glass` | a `str` message |
+| **Look** | `Fluksio`, `Material` or `Glass` | a `str` message |
 | **Theme** | `System`, `Light` or `Dark` | a `str` message |
 | **Palette** | the dashboard's colours, in order | a `list` message |
 | **Background** | the URL of an image | a `str` message |
@@ -130,11 +130,14 @@ locking a panel down remotely.
 
 ### Look
 
-**Material** lays flat, tonal cards on a plain ground. **Glass** floats
-translucent tiles over a soft, slowly moving one. They are two complete sets of
-components, not two stylesheets — but they are the same dashboard: every widget,
-every control and every keystroke behaves identically, so switching look never
-changes what a panel can do.
+**Fluksio** is the app's own design — `--card` surfaces separated by a hairline
+and a low shadow, pill controls, one slate-blue accent — and is what a dashboard
+wears until you choose otherwise. **Material** lays flat, tonal cards on a plain
+ground. **Glass** floats translucent tiles over a soft, slowly moving one.
+
+They are three complete sets of components, not three stylesheets — but they are
+the same dashboard: every widget, every control and every keystroke behaves
+identically, so switching look never changes what a panel can do.
 
 ### Palette