Stop the press that starts a drag from deselecting what it grabbed

Dragging a selection of forty photographs onto a collection filed one.

Selection mode reports every press as a ctrl-press — deliberately, so
touch and pointer go through one set of rules rather than two — and ctrl
toggled. So the press that took hold of one of the forty took it *out*
of the selection on the way down. `drag-started` then looked at the cell
under the finger, found it unselected, and did exactly what it is meant
to do with an unselected cell: made it the whole selection and carried
it alone. The only sign was the grabbed cell's ring blinking out at the
moment the user began to move.

A plain press has never had this problem, because pressing an
already-selected cell has always been documented to leave the selection
alone — for precisely this reason. Ctrl now does the same: adding still
happens on the press, since the drag reads the selection immediately,
but *removing* is handed back as `Press::Deferred` and applied by the
click. Slint reports a click only for a press that stayed within
`tap-slop`, so a tap still toggles and a drag never does.

The unit tests now go through a `click` helper — a press and the release
that follows it — because that is the only thing a user can perform, and
calling `apply_press` alone would assert against half the policy.

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

ui/dr-ui/src/library_ui.rs

@@ -4562,6 +4562,12 @@ pub fn wire<F>(
         let coll_for_click = coll_ctl.clone();
         let on_open_image = on_open_image.clone();
         window.on_library_cell_clicked(move |i| {
+            let Some(w) = weak.upgrade() else { return };
+
+            // The press stayed put, so it was a tap and not a drag: whatever it
+            // held back can be applied now. See `collections_ui::Press`.
+            crate::collections_ui::commit_press(&w, &coll_for_click, &ctl.visible_ids());
+
             // A ctrl- or shift-click is a selection gesture. Opening the image
             // too would throw the user out of the grid mid-selection.
             if coll_for_click.press_was_modified() {
@@ -4572,16 +4578,12 @@ pub fn wire<F>(
             if let Some(path) = path {
                 // Leave the grid for the develop view. The status bar's
                 // "‹ Library" button comes back here.
-                if let Some(w) = weak.upgrade() {
-                    w.set_show_library(false);
-                    // Which cell the develop view is now showing, so the photo
-                    // roll opens marking it rather than marking nothing.
-                    w.set_library_roll_current(i);
-                }
+                w.set_show_library(false);
+                // Which cell the develop view is now showing, so the photo
+                // roll opens marking it rather than marking nothing.
+                w.set_library_roll_current(i);
                 on_open_image(path);
-                if let Some(w) = weak.upgrade() {
-                    report_position(&w, &ctl, i as usize);
-                }
+                report_position(&w, &ctl, i as usize);
             }
         });
     }