Draw the date histogram over the collection you are looking at

The timeline counted the whole library whatever the grid was showing, so
opening a collection left a fortnight in Arosa as one column of a
fifteen-year axis — an axis describing photographs that were not on
screen.

Scope the buckets and the span to the same collection and rating filter
the grid uses. `timeline_range` counts `images` alone and cannot express
the membership join, so the scoped query lives beside the other scoped
readers in the UI and shares their descendants-of-scope rule.

`catalog_span` now delegates to the same scoped reader. Zoom and scrub
measured the full library while the bars were scoped, so a scrub could
land on an instant the collection did not contain and send the view
somewhere the user had not asked to go.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

core/dr-catalog/src/lib.rs

@@ -96,7 +96,10 @@ impl Granularity {
     /// Applied to **local** time, not UTC: "everything from 3 August" means
     /// the photographer's 3 August, which is why `captured_offset` is stored
     /// alongside the UTC timestamp.
-    fn strftime(self) -> &'static str {
+    /// Public so a caller that must build its own bucketing query — one
+    /// joining collection membership, say — buckets identically to
+    /// [`Catalog::timeline_range`] rather than reimplementing the format.
+    pub fn strftime(self) -> &'static str {
         match self {
             Granularity::Year => "%Y",
             Granularity::Month => "%Y-%m",