Swipes take a longer drag and slide the reader across (#49)

At a flat 60px, a thumb scrolling slightly on the diagonal moved on to the next item by
accident. A swipe now has to cover a quarter of the reader's width, and never less than 100px,
and the reader follows the finger while it is down, so it is plain before letting go whether it
will move on. It slides off on a swipe and the next item slides in from the other side; a short
one springs back. The CHANGELOG also gets back the [0.8.3] link a stray edit had broken.

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

tests/ui/app.spec.js

@@ -1231,6 +1231,9 @@ test.describe('touch gestures on a phone', () => {
     const shown = page.locator('#detail .dt');
     await expect(shown).toHaveText(titles[0]);
 
+    await drag(page, { x: 300, y: 400 }, { x: 230, y: 410 });     // too short: stays (#49)
+    await expect(shown).toHaveText(titles[0]);
+    await expect(page.locator('#detail')).not.toHaveAttribute('style', /translate/);  // springs back
     await drag(page, { x: 300, y: 400 }, { x: 80, y: 410 });      // left: the next item
     await expect(shown).toHaveText(titles[1]);
     await drag(page, { x: 300, y: 400 }, { x: 80, y: 410 });      // left on the last: stays