refactor(cine): expose slice from useViewLocator

Each tool was destructuring {locator, frame} from useViewLocator and
then re-deriving slice via locatorPatch(locator.value).slice. The
composable already computes slice internally; surface it directly so
the three tool files drop a redundant computed each.

Author: PaulHax

src/components/tools/polygon/PolygonTool.vue

@@ -178,8 +178,7 @@ export default defineComponent({
     const activeToolStore = useActiveToolStore();
     const { activeLabel } = storeToRefs(activeToolStore);
 
-    const { locator, frame } = useViewLocator(viewId, imageId);
-    const slice = computed(() => locatorPatch(locator.value).slice);
+    const { locator, frame, slice } = useViewLocator(viewId, imageId);
 
     const { metadata: imageMetadata } = useImage(imageId);
     const isToolActive = computed(() => toolStore.currentTool === toolType);

src/components/tools/rectangle/RectangleTool.vue

@@ -71,8 +71,7 @@ export default defineComponent({
     const activeToolStore = useActiveToolStore();
     const { activeLabel } = storeToRefs(activeToolStore);
 
-    const { locator, frame } = useViewLocator(viewId, imageId);
-    const slice = computed(() => locatorPatch(locator.value).slice);
+    const { locator, frame, slice } = useViewLocator(viewId, imageId);
 
     const { currentImageID } = useCurrentImage();
     const isToolActive = computed(() => toolStore.currentTool === toolType);

src/components/tools/ruler/RulerTool.vue

@@ -66,11 +66,7 @@ export default defineComponent({
     const rulerStore = useRulerStore();
     const { activeLabel } = storeToRefs(rulerStore);
 
-    const { locator, frame } = useViewLocator(viewId, imageId);
-    const slice = computed(() => {
-      const patch = locatorPatch(locator.value);
-      return patch.slice;
-    });
+    const { locator, frame, slice } = useViewLocator(viewId, imageId);
 
     useImage(imageId);
     const isToolActive = computed(() => toolStore.currentTool === Tools.Ruler);

src/composables/useViewLocator.ts

@@ -34,5 +34,5 @@ export function useViewLocator(
     })
   );
 
-  return { locator, frame };
+  return { locator, frame, slice };
 }