Swipe between items like turning pages (#52)

On a phone the reader is fixed over the item list, and the swipe from #49 moved it alone and
faded it to 40%, so the list showed through it and in the strip it uncovered, and again as the
next item slid in from the far side. Now a layer beside the reader, #dpeek, holds what is really
there: the next or previous item, drawn by the same detailHtml the reader uses, with 16px of the
page's background between them; "No more items" past the last; or, swiping right from the
first, a dimmer over the list that lifts as the reader, shadowed along its edge, is drawn off.
On release the swipe carries on from where the finger left it, over 120-250ms by how far is
left, and the neighbour becomes the reader in place; with reduced motion it switches at once.

A touch starting within 14px of the left edge is kept from Safari, which otherwise takes it as
Back and leaves the page mid-swipe. 14px because the back button starts at 16.

Offsets are rounded to whole pixels: at a fractional offset the seam between the reader and its
neighbour drew a stray light line.

The design had the list shift a third of the way across as it is uncovered, as iOS does. #detail
lives inside #shell, and a transform there makes it the containing block for the fixed reader,
so that part is left out; the dimmer and shadow carry it.

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

CHANGELOG.md

@@ -27,6 +27,11 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Swiping to the next or previous item takes a longer swipe, a quarter of the screen, so a
   diagonal scroll no longer jumps ahead by accident. The item follows your finger and slides
   across as it changes.
+- Swiping between items on a phone no longer shows the item list through the reader. The next
+  or previous item sits beside the one you are reading and comes across with it, the end of the
+  list says so, and swiping right from the first item draws the reader off the list, dimmed
+  until it is uncovered. A swipe from the screen's left edge stays with the page, rather than
+  Safari taking it as Back.
 
 ## [0.8.4] - 2026-09-19