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/tests/widgets.spec.ts

@@ -626,14 +626,14 @@ async function setLook(
   })
 }
 
-// Both looks, in both themes. A look is mostly colour and depth, so the four
-// screenshots are the assertion that neither collapses — and the checks around
-// them are that a look changes how the panel is drawn and nothing else.
+// Every look, in both themes. A look is mostly colour and depth, so the
+// screenshots are the assertion that none of them collapses — and the checks
+// around them are that a look changes how the panel is drawn and nothing else.
 for (const scheme of ["light", "dark"] as const) {
   test.describe(`${scheme} theme`, () => {
     test.use({ colorScheme: scheme })
 
-    for (const look of ["material", "glass"] as const) {
+    for (const look of ["fluksio", "material", "glass"] as const) {
       test(`the panel reads in ${scheme} ${look}`, async ({ page }) => {
         await openPanel(page)
         await setLook(page, dashboardName, { look: { value: look } })
@@ -691,7 +691,7 @@ for (const scheme of ["light", "dark"] as const) {
         path: `screenshots/widgets/${scheme}-palette.png`,
       })
       await setLook(page, dashboardName, {
-        look: { value: "material" },
+        look: { value: "fluksio" },
         palette: { value: [] },
       })
     })