Merge: mask a whole category, not just one instance

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

# Conflicts:
#	apps/darkroom-desktop/Cargo.toml
#	docs/traceability.md

ui/dr-ui/ui/app.slint

@@ -1,6 +1,6 @@
 import { Theme } from "theme.slint";
 import { AdjustPanel, GeometryPanel, GroupStrip, ParamRow, TransferPanel, ViewMode } from "adjust.slint";
-import { GradientHandle, GradientHandles, HandleRole, MaskPanel, MaskRow, SubjectRow } from "masks.slint";
+import { CategoryRow, GradientHandle, GradientHandles, HandleRole, MaskPanel, MaskRow, SubjectRow } from "masks.slint";
 import { SpotHandle, SpotHandles, SpotPanel, SpotRole } from "spots.slint";
 import { CropOverlay } from "crop.slint";
 import { HistoryPanel, HistoryRow } from "history.slint";
@@ -985,6 +985,7 @@ export component AppWindow inherits Window {
 
     in property <[MaskRow]> mask-rows;
     in property <[SubjectRow]> subject-rows;
+    in property <[CategoryRow]> category-rows;
     in property <bool> segmented: false;
     in property <bool> segmenting: false;
     in property <bool> refining: false;
@@ -1068,6 +1069,7 @@ export component AppWindow inherits Window {
     callback mask-morph-radius-changed(string, float);
     callback add-gradient-mask(bool);
     callback add-subject-mask(int);
+    callback add-category-mask(string);
 
     /// Whether the develop column — image info, geometry, adjust — is shown.
     ///
@@ -2510,6 +2512,7 @@ in property <bool> panel-visible: true;
                                 enabled: root.adjust-enabled;
                                 masks: root.mask-rows;
                                 subjects: root.subject-rows;
+                                categories: root.category-rows;
                                 segmented: root.segmented;
                                 segmenting: root.segmenting;
                                 refining: root.refining;
@@ -2543,6 +2546,7 @@ in property <bool> panel-visible: true;
                                 }
                                 add-gradient(radial) => { root.add-gradient-mask(radial); }
                                 add-subject(i) => { root.add-subject-mask(i); }
+                                add-category(n) => { root.add-category-mask(n); }
                             }
 
                             if root.local-mode: Rectangle {