Say that a tablet's scrollers show a position cue

The manual said the lists on a tablet scroll by flick alone, and
outstanding.md §4a that Android had no scrollbars by design. Both now
describe the cue from #69: a thin line while the view moves, gone once
it stops, that a flick starting on it passes through; and §4a notes
DR_SCROLL_CUE for looking at it on a desktop, and that it is not yet
checked on the tablet. The bundled manual is regenerated to match.

docs/dev/outstanding.md

@@ -226,8 +226,11 @@ decoder behind a trait (FR-RAW-2), and duplicate originals (FR-CAT-11a, §2 abov
   false alarm on the common path would teach the notice to be dismissed unread.
 
 The desktop's scrollbars (the develop column, the grid, the sidebar, Settings, the film list and
-the help sheet) are drawn only where `dr_plat::is_touch_first()` is false; on Android the lists
+the help sheet) are drawn only where `dr_plat::is_touch_first()` is false. On Android the same
-still scroll by flick alone, which is deliberate rather than outstanding.
+scrollers show instead a 3 px position cue (#69): `Scrolling.cue` in `widgets.slint`, the thumb
+alone, drawn while the viewport moves and faded 500 ms after, with no touch target, so a flick that
+starts on it scrolls the list (`tests/scroll_cue.rs`). A desktop build shows the cue when
+`DR_SCROLL_CUE=1` is set, for checking it without a device. Not yet checked on the tablet.
 
 ---
 

docs/manual/README.md

@@ -71,7 +71,9 @@ Drag the timeline to scrub through years; Ctrl and the wheel resize the
 thumbnails. On a desktop a scrollbar beside the grid says how far through the
 library the view is — drag its thumb, or click the track to move a page — and
 the sidebar, the develop column and Settings have one too whenever they run
-past the window. On a tablet they scroll by flick alone.
+past the window. On a tablet they scroll by flick alone, and a thin line at
+the right-hand edge shows where the view is while it moves, fading once it
+stops; it is only a picture, and a flick that starts on it scrolls the list.
 
 `Help` in the header, or `F1`, opens the controls and shortcuts: every key and
 gesture, screen by screen, with `See it` beside those this page shows, and

docs/manual/index.html

@@ -191,7 +191,9 @@ and the same keys work there.</p>
 thumbnails. On a desktop a scrollbar beside the grid says how far through the
 library the view is — drag its thumb, or click the track to move a page — and
 the sidebar, the develop column and Settings have one too whenever they run
-past the window. On a tablet they scroll by flick alone.</p>
+past the window. On a tablet they scroll by flick alone, and a thin line at
+the right-hand edge shows where the view is while it moves, fading once it
+stops; it is only a picture, and a flick that starts on it scrolls the list.</p>
 <p><code>Help</code> in the header, or <code>F1</code>, opens the controls and shortcuts: every key and
 gesture, screen by screen, with <code>See it</code> beside those this page shows, and
 <code>Manual</code> to open this page. In develop it is the <code>?</code> beside <code>Settings</code>.</p>