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.

frontend/src/components/Dashboard/panels.tsx

@@ -1421,10 +1421,12 @@ export function DashboardPanel({
               onChange={(setting) => setSetting("look", setting)}
             />
             <p className="text-sm text-muted-foreground">
-              How this dashboard is drawn. Glass floats translucent tiles over a
-              soft moving ground; Material lays flat tonal cards on a plain one.
-              The widgets are the same either way — a look changes what they
-              look like and nothing about what they do.
+              How this dashboard is drawn. Fluksio is the app's own design, and
+              what a dashboard wears until you choose otherwise; Material lays
+              flat tonal cards on a plain ground; Glass floats translucent tiles
+              over a soft moving one. The widgets are the same whichever you
+              pick — a look changes what they look like and nothing about what
+              they do.
             </p>
           </div>