Drag the date range on the axis it is chosen from

The range could be turned on with a finger and not aimed with one. Its two
ends were typed as `YYYY-MM-DD` into 108px fields behind a soft keyboard, to
name days already drawn on the axis a thumb away; and the chip that seeds them
takes its span from the timeline's zoom and pan, which are a wheel and a middle
button. A touch screen has neither, so on Android the filter was a switch with
no aim.

The band is now on the timeline. Two ends with grips, dragged along the bars,
released to filter — the histogram was already how a period is found, and this
makes it how a period is stated. Both ends snap to whole days, which is what
the typed fields mean, what `show_range` reads back out, and a floor under a
range dragged shut. The fields stay for what dragging cannot do: name an exact
day, and say in words what the range is.

For that to work the axis had to stop following the range. Redrawn to the band,
it moved the ground under the very handles doing the narrowing, and there was
nothing outside the range left to widen back into.

While there: a fixed number of equal bins instead of calendar buckets. Between
one calendar unit and the next the bar count is free to wander by a factor of
twelve, so zooming in halved it two steps out of three — the same picture drawn
wider until it jumped back to fine. Equal bins also include the empty ones, so
a bar's position on the track and the date under it are finally the same
quantity; before, a library with gaps drew a February six months wide and the
marker, the band and a click all pointed somewhere else. The count is a
setting, 32 or 64, because the right answer is a question about the screen.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

ui/dr-ui/src/settings_ui.rs

@@ -26,8 +26,8 @@ use std::rc::Rc;
 
 use dr_types::settings::budget;
 use dr_types::{
-    CollisionPolicy, ColourSpace, ExportFormat, ExportTarget, OutputSharpening, Settings,
-    SizingMode,
+    CollisionPolicy, ColourSpace, ExportFormat, ExportTarget, LibrarySettings, OutputSharpening,
+    Settings, SizingMode,
 };
 use slint::ComponentHandle;
 
@@ -146,6 +146,23 @@ pub fn render(window: &AppWindow, controller: &SettingsController) {
     window.set_settings_copy_includes_framing(s.develop.copy_includes_framing);
     window.set_settings_cache_usage(controller.usage_label.borrow().clone().into());
 
+    // --- library -------------------------------------------------------
+    //
+    // Labelled here rather than in the page, so the chips cannot offer a count
+    // the record does not: `BAR_CHOICES` is what `sanitise` snaps a
+    // hand-edited file to, and a third chip drawn beside them would be a
+    // choice that silently became one of the other two.
+    window.set_settings_timeline_bar_labels(slint::ModelRc::new(slint::VecModel::from(
+        LibrarySettings::BAR_CHOICES
+            .iter()
+            .map(|n| slint::SharedString::from(n.to_string()))
+            .collect::<Vec<_>>(),
+    )));
+    window.set_settings_timeline_bars_selected(index_of(
+        &LibrarySettings::BAR_CHOICES,
+        &s.library.timeline_bars,
+    ));
+
     // --- export --------------------------------------------------------
     //
     // Choice rows are sent as labels plus the selected index rather than as a
@@ -404,6 +421,18 @@ where
         });
     }
 
+    {
+        let weak = window.as_weak();
+        let ctl = controller.clone();
+        window.on_settings_timeline_bars_picked(move |i| {
+            let Some(w) = weak.upgrade() else { return };
+            if let Some(n) = LibrarySettings::BAR_CHOICES.get(i as usize).copied() {
+                ctl.edit(|s| s.library.timeline_bars = n);
+            }
+            render(&w, &ctl);
+        });
+    }
+
     {
         let weak = window.as_weak();
         let ctl = controller.clone();