Enhance BranchSelection component to force re-render on branch list change

- Added a computed property `branchesKey` to generate a unique key based on branch IDs, ensuring the dropdown re-renders when the branch list updates.
- Updated the FormattedDropdown component to utilize this key for improved responsiveness to data changes.

frontend/src/components/falukant/BranchSelection.vue

@@ -3,6 +3,7 @@
     <h3>{{ $t('falukant.branch.selection.title') }}</h3>
     <div>
       <FormattedDropdown
+        :key="branchesKey"
         :options="branches"
         :columns="branchColumns"
         v-model="localSelectedBranch"
@@ -54,6 +55,12 @@ export default {
       ],
     };
   },
+  computed: {
+    // Erzwingt ein Neu-Rendern des Dropdowns, wenn sich die Branch-Liste ändert
+    branchesKey() {
+      return this.branches.map(b => b.id).join('-');
+    },
+  },
   watch: {
     selectedBranch(newVal) {
       this.localSelectedBranch = newVal;