Directly patch posterminalIds in Redux instead of reloading the category tree

After toggling a POS category, update the category's posterminalIds array
in-place rather than re-fetching the entire tree. This keeps the settings
cycle open on the same terminal. Also fix off-by-one in terminal cycling
and ensure posterminals load on category page mount.

src/store/categorySlice.js

@@ -291,6 +291,17 @@ const categorySlice = createSlice({
     resetCategoryState() {
       return initialState;
     },
+    patchCategoryPosterminalIds(state, action) {
+      const { categoryId, terminalId, enabled } = action.payload;
+      const cat = state.categories?.[String(categoryId)];
+      if (!cat) return;
+      if (!Array.isArray(cat.posterminalIds)) cat.posterminalIds = [];
+      if (enabled && !cat.posterminalIds.includes(terminalId)) {
+        cat.posterminalIds.push(terminalId);
+      } else if (!enabled) {
+        cat.posterminalIds = cat.posterminalIds.filter((id) => id !== terminalId);
+      }
+    },
     setRenameMode(state, action) {
       state.renameMode = Boolean(action.payload);
     },
@@ -451,6 +462,7 @@ export const {
   setRenameMode,
   removeArticleBySku,
   patchArticleInLists,
+  patchCategoryPosterminalIds,
 } = categorySlice.actions;
 
 export const selectRenameMode = (state) => state.category.renameMode;