Rate under the pointer, filter a star range, and name Help as help

Rating keys in the grid follow darktable's rule: with the pointer over a
photograph outside the selection, 0-5, P, X and U judge that photograph
alone; over one inside it, the whole selection, as before; off the grid,
the selection. The hover is cleared when the grid scrolls, so a key after
a wheel turn cannot judge whatever used to be under the pointer.

Holding F and tapping digits filters by stars: one digit for exactly
that many, two for everything between them, F alone to show every
rating again. The filter gains a ceiling to do it (`max_rating`, one
BETWEEN in the query). The place record carries it, and a record from an
older build reads as having none. The star chips light across a capped
range and the bar says "2-3★ only" beside them.

The grid also takes Ctrl+E and Ctrl+Shift+E for the selection, Ctrl+V to
paste onto it and Ctrl+A to select all. The "Gestures" button is now
"Help", its sheet "Controls and shortcuts", and F1 opens it.

ui/dr-ui/src/library_ui/ratings_keywords.rs

@@ -931,16 +931,23 @@ pub(super) fn wire_ratings_and_flags(
     }
 
     // A rating or flag key. Applies to the whole selection, which is what
-    // makes judging a run of frames one keystroke rather than forty.
+    // makes judging a run of frames one keystroke rather than forty — unless
+    // the pointer is over a photograph outside it, which then takes the key
+    // alone (darktable's rule; see `judged_images`).
     {
         let weak = window.as_weak();
         let ctl = ctl.clone();
         let coll_for_keys = coll_ctl.clone();
         window
             .global::<Library>()
-            .on_library_judged(move |rating, flag| {
+            .on_library_judged(move |rating, flag, hovered| {
                 let Some(w) = weak.upgrade() else { return };
-                let chosen = coll_for_keys.selected();
+                let offset = w.global::<Library>().get_library_offset().max(0) as usize;
+                let under_pointer = usize::try_from(hovered)
+                    .ok()
+                    .and_then(|ordinal| ordinal.checked_sub(offset))
+                    .and_then(|row| ctl.visible_ids().get(row).copied());
+                let chosen = judged_images(coll_for_keys.selected(), under_pointer);
 
                 // Exactly one axis is meant per keystroke; the other arrives as
                 // -1 so a star press cannot disturb a flag or the reverse.
@@ -953,6 +960,24 @@ pub(super) fn wire_ratings_and_flags(
     }
 }
 
+/// TRACES: FR-UI-5
+/// What a judgement key applies to: the photograph under the pointer when it
+/// is not part of the selection, and the selection otherwise.
+///
+/// Hovering one of the selected frames rates all of them, so the pointer
+/// resting on the grid never shrinks a forty-frame judgement to one. With
+/// the pointer off the grid, or over a cell the grid has since scrolled away
+/// from, it is the selection as it always was.
+fn judged_images(
+    selection: Vec<dr_types::ImageId>,
+    under_pointer: Option<dr_types::ImageId>,
+) -> Vec<dr_types::ImageId> {
+    match under_pointer {
+        Some(id) if !selection.contains(&id) => vec![id],
+        _ => selection,
+    }
+}
+
 /// --- keywords (FR-CAT-5, FR-CAT-6) ------------------------------------
 ///
 /// Three callbacks and no state of their own: the sheet's open/shut is local
@@ -1003,6 +1028,27 @@ pub(super) fn wire_keywords(
 mod tests {
     use super::*;
 
+    // --- what a judgement key reaches (FR-UI-5) ----------------------------
+
+    #[test]
+    fn a_hovered_photograph_outside_the_selection_is_judged_alone() {
+        let (a, b, c) = (dr_types::ImageId(1), dr_types::ImageId(2), dr_types::ImageId(3));
+        assert_eq!(judged_images(vec![a, b], Some(c)), vec![c]);
+    }
+
+    #[test]
+    fn hovering_a_selected_photograph_judges_the_whole_selection() {
+        let (a, b) = (dr_types::ImageId(1), dr_types::ImageId(2));
+        assert_eq!(judged_images(vec![a, b], Some(b)), vec![a, b]);
+    }
+
+    #[test]
+    fn with_nothing_hovered_the_selection_is_judged() {
+        let (a, b) = (dr_types::ImageId(1), dr_types::ImageId(2));
+        assert_eq!(judged_images(vec![a, b], None), vec![a, b]);
+        assert_eq!(judged_images(vec![], None), vec![]);
+    }
+
     // --- what the status line says about a keyword (FR-CAT-5) -------------
     //
     // Split out from the callback for the same reason `decide_drop` is: the