LR-VIEW-PHOTOGRID: group the photo/square grid by date with day/month/year headers

Catalog date runs (stacks never split), Sort.group (auto/day/month/year/none) in the sort
menus, library.groups query, sticky headers, header click selects the group; layout unit
tests and a headless test.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

crates/engine/src/tests_libops.rs

@@ -0,0 +1,34 @@
+//! Library management commands: date groups, keyword rename/delete/merge, batch rename, capture
+//! time, label names, import review.
+
+use serde_json::json;
+
+use crate::Session;
+
+/// Date headers follow the grid order and the sort's grouping.
+#[test]
+fn date_groups_follow_sort_and_grouping() {
+    let mut s = Session::with_demo();
+    let vis = s.visible_cloned();
+    let g = s.execute("library.groups", &json!({})).unwrap();
+    let groups = g.as_array().unwrap();
+    assert!(groups.len() > 3, "{g}");
+    let total: u64 = groups.iter().map(|x| x["count"].as_u64().unwrap()).sum();
+    assert_eq!(total as usize, vis.len());
+    // contiguous runs in grid order, labelled with weekday and date
+    let mut next = 0;
+    for x in groups {
+        assert_eq!(x["start"].as_u64().unwrap(), next);
+        next += x["count"].as_u64().unwrap();
+        assert!(x["label"].as_str().unwrap().contains(", "), "{x}");
+    }
+    let months = s.execute("library.groups", &json!({"by": "month"})).unwrap();
+    assert!(months.as_array().unwrap().len() < groups.len());
+    assert_eq!(months[0]["key"].as_str().unwrap().len(), 7);
+    s.execute("library.sort", &json!({"group": "none"})).unwrap();
+    assert_eq!(s.execute("library.groups", &json!({})).unwrap(), json!([]));
+    s.execute("library.sort", &json!({"group": "year", "key": "fileName"})).unwrap();
+    assert_eq!(s.execute("library.groups", &json!({})).unwrap(), json!([]), "no date headers when sorting by name");
+    assert_eq!(s.sort.group, lightcraft_catalog::GroupBy::Year);
+    assert!(s.execute("library.sort", &json!({"group": "week"})).is_err());
+}