DeadAir's pause on a slider, shown only while DeadAir is on (#183)

The four segmented buttons gave no sense that 0.2 to 0.5 s is one scale,
and stayed on screen with DeadAir off, where they did nothing. A range
input with a dot at each stop and Brisk/Relaxed at its ends says both.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/ui/app.spec.js

@@ -1782,8 +1782,8 @@ test('DeadAir is off until turned on for a show, then plays it shortened, with y
   // A longer pause of your own (#182) saves less.
   const usual = (await entry()).enclosures[0].deadair;
   await page.locator('#content .acts [data-a="settings"]').click();
-  await expect(page.locator('[name=sdpause][value="300"]')).toBeChecked();
-  await page.locator('[name=sdpause][value="500"]').locator('xpath=..').click();
+  await expect(page.locator('#sdpause')).toHaveValue('300');
+  await page.locator('#sdpause').fill('500');
   await page.locator('#ssave').click();
   await expect.poll(async () => (await entry()).enclosures[0].deadair).toBeLessThan(usual);