Show and set colour labels in the grid and develop, and filter by them

Colour labels could be read from a Lightroom sidecar and queried by the
selector, but nothing drew one or set one, so the only labels a library
held were ones another program had written.

Every mark carries its label's initial on its colour — R, Y, G, B, P —
so a label is read without telling red from green, which is what
NFR-A11Y-3 asks of colour labels by name. A grid cell shows the mark
before its filename. In the grid, 6, 7, 8 and 9 set red, yellow, green and
blue as Lightroom's keys do, on the photograph under the pointer or on
the selection by the rule the star keys follow; the same key again takes
the label off, and over a mixed selection it sets it on all. The
selection bar gains Label, which opens the six choices — each a mark and
a name — and purple, which has no key, is there. In develop the top bar
says "Label: Green" beside the mark, opens the same choices, and 6-9
label the open photograph.

Each gesture is one catalog transaction, then the grid, the counts and
both sidecars are written as a rating's are. The filter bar gains a chip
per label, its mark and its name with a count, one at a time; the filter
is one SQL term, travels in the place record, and "All" clears it.

ui/dr-ui/src/library/scan.rs

@@ -914,15 +914,24 @@ mod tests {
     fn a_label_from_another_device_reaches_the_catalog_and_none_clears_nothing() {
         // TRACES: FR-CAT-5
         let cat = library(&["2026/a.CR2"]);
-        assert_eq!(apply_judgement(cat.connection(), 1, "2026/a.drsc", 0, 0, 4).unwrap(), 1);
+        assert_eq!(
+            apply_judgement(cat.connection(), 1, "2026/a.drsc", 0, 0, 4).unwrap(),
+            1
+        );
         let label = |cat: &Catalog| -> Option<i64> {
             cat.connection()
-                .query_row("SELECT label FROM versions WHERE is_default = 1", [], |r| r.get(0))
+                .query_row("SELECT label FROM versions WHERE is_default = 1", [], |r| {
+                    r.get(0)
+                })
                 .unwrap()
         };
         assert_eq!(label(&cat), Some(4));
         apply_judgement(cat.connection(), 1, "2026/a.drsc", 3, 0, 0).unwrap();
-        assert_eq!(label(&cat), Some(4), "a sidecar with no label left it alone");
+        assert_eq!(
+            label(&cat),
+            Some(4),
+            "a sidecar with no label left it alone"
+        );
     }
 
     /// The regression, in one line: a rating in a sidecar reaches the grid.