slides: the slide list steps aside once you have picked a slide

[iamgeo92]

The problem

Below 700px the side panels are not columns — styles.css deliberately turns
them into overlay drawers laid across the canvas:

/* Panels become OVERLAY DRAWERS. As flex siblings the 188px sidebar left a
   214px canvas on a 402px screen — the thing you are editing became the
   smallest thing on screen. */
.ed-sidebar, .ed-props { position: absolute; top: 0; bottom: 0; z-index: 40; … }

That is the right call. But the thumbnail click handler was written for the
column layout:

item.addEventListener('click', () => this.store.goTo(i))

So on a phone, tapping a slide navigated correctly and then left the drawer
sitting on top of the slide it had just navigated to. Every slide change
cost a second trip to the ☰ toggle in the topbar just to see what you picked.

The fix

The drawer steps aside when you pick from it.

Closing is scoped two ways, so nothing changes where the panel is not a drawer:

• By width — only when the panel is actually an overlay (≤700px, the same
  threshold the CSS and applyPhoneChrome already use). On a wide screen the
  list is a real column beside the canvas and stays exactly where it is.
• By target — only the thumbnail itself. The per-thumbnail Duplicate and
  Delete buttons already stopPropagation, so editing the list never
  dismisses it. Those are edits to the list, not a choice of slide.

Before / after

Same gestures both sides: open ☰, tap slide 3.

before — the list covers the slide you just chose	after — the drawer steps aside

In the "before" clip you can see the extra step the old behaviour forced: find
☰ again, press it, then look at your slide.

How this was verified

Dev server, Chrome DevTools iPhone emulation (390×664, DPR 3, hasTouch) with
real touch dispatch, plus a 1280×800 mouse context for the desktop cases:

case	result
drawer starts closed on a phone	pass
☰ opens the drawer	pass
picking a slide closes the drawer	pass
the deck navigated to the slide that was tapped (not just closed)	pass
Duplicate on a thumbnail adds a slide and leaves the drawer open	pass
desktop: sidebar is a column and starts open	pass
desktop: picking a slide leaves it open	pass

Gates:

node_modules/.bin/tsc -b                                        clean
npm run build:single                                            ok (664KB shell)
node scripts/shell-gate.mjs …/Bento_Slides.bento.html           splice contract OK

No new user-facing strings, so no i18n catalog changes. No format or kernel
change; nothing under sync/.

Scope note: this PR deliberately covers only picking a slide. Dismissing a
drawer by tapping the canvas outside it is a separate gap and a separate PR, so
the two do not tangle in review.

Caveat: verified under Chromium's iPhone emulation rather than on physical
iOS hardware. This change is layout-threshold and event-target logic with no
WebKit-specific behaviour in it, so the risk of an emulation-only result is low.

---

Changelog entry — not in the diff, on purpose

CHANGELOG.md is this repo's named conflict magnet (docs/PARALLEL-WORK.md §3). With several of these open at once, and [Unreleased] being emptied every time a release is cut, a changelog hunk made every one of them conflict on that file and nothing else — twice over. They carry no CHANGELOG.md change so they stay mergeable; here is the entry to drop in at release time, or I'll add it back in whatever form you prefer.

- **Picking a slide on a phone now shows you the slide.** Below 700px the slide
  list is not a column beside the canvas — it is a drawer laid over it. Tapping
  a thumbnail navigated correctly and then left the list sitting on top of the
  answer, so every slide change cost a second trip to the ☰ toggle to see what
  you had chosen. The drawer now steps aside when you pick from it. On a wide
  screen the list is a real column and rightly stays where it is, and the
  per-thumbnail Duplicate and Delete buttons leave it open on every width —
  those are edits to the list, not a choice of slide.

[iamgeo92]

@nyblnet — review whenever suits you.

Small one: below 700px the slide list is an overlay drawer (which is the right call — the CSS comment explains why), but tapping a thumbnail left it sitting on top of the slide it had just navigated to, so every slide change cost a second trip to ☰.

Scoped two ways so nothing changes elsewhere: only while the panel is a drawer, and only from the thumbnail itself — the per-thumb Duplicate/Delete already stop propagation, so editing the list never dismisses it.

One file, +25/−1. #273 is stacked on this one.