Draw the colour disc inside its tile rather than past it

The disc was sized against its parents in percentages, and every box
between it and the tile is sized by what is in it — so the chain never
resolved, the brightness slider grew, and the tile scrolled with half a
disc showing. Container units are the tile's own height whatever sits in
between, so the widget now fits exactly.

Two guards behind it, since both are things a picture can fail silently:
nothing on a panel of pictures may overflow its tile, and Touch has to
actually make a control bigger while leaving what it publishes alone.

frontend/tests/widgets.spec.ts

@@ -306,6 +306,22 @@ test("rows are drawn in the order they were configured", async ({ page }) => {
   await expect(rows.nth(2)).toContainText(/grid/i)
 })
 
+test("a widget is drawn inside its tile rather than scrolled", async ({
+  page,
+}) => {
+  await openPanel(page)
+
+  // A picture that overflows its tile is a picture nobody can see the rest of.
+  // Only the widgets that are text or a list may scroll, and this panel holds
+  // none of them — so nothing here should.
+  const overflowing = await page.evaluate(() =>
+    [...document.querySelectorAll(".dui-frame-body")]
+      .filter((body) => body.scrollHeight > body.clientHeight + 1)
+      .map((body) => body.closest("[data-testid=widget-frame]")?.textContent),
+  )
+  expect(overflowing, "these widgets overflow their tile").toEqual([])
+})
+
 test("the icon follows what the message says", async ({ page }) => {
   await openPanel(page)
   const glyph = page.getByTestId("icon-glyph")
@@ -461,6 +477,37 @@ test("a chart's cursor follows the pointer", async ({ page }) => {
   ).toBeLessThan(3)
 })
 
+test("touch makes the controls bigger without changing what they do", async ({
+  page,
+}) => {
+  await openPanel(page)
+  const control = page.getByTestId("widget-frame").filter({ hasText: "Mode" })
+  const pointer = (await control.getByRole("button").first().boundingBox())!
+    .height
+
+  await setLook(page, dashboardName, { touch: { value: true } })
+  await openPanel(page)
+  await expect(page.getByTestId("canvas-surface")).toHaveAttribute(
+    "data-touch",
+    "",
+  )
+  const touched = (await control.getByRole("button").first().boundingBox())!
+    .height
+  expect(
+    touched,
+    `a segment is ${touched.toFixed(1)} touched and ${pointer.toFixed(1)} pointed at`,
+  ).toBeGreaterThan(pointer)
+
+  // The control is the same control: it still publishes what it always did.
+  await control.getByRole("button", { name: "Boost" }).click()
+  await expect(control.getByRole("button", { name: "Boost" })).toHaveAttribute(
+    "aria-pressed",
+    "true",
+  )
+
+  await setLook(page, dashboardName, { touch: { value: false } })
+})
+
 /**
  * What a dashboard was told to wear, as a wall panel would be told.
  *