Center sort, settings, and delete buttons in FilterList header

Use two v-spacers (before and after the button group) to center the
sort, settings, and delete buttons between the Type Filter title and
the right edge. This matches the main branch pattern and keeps the
buttons clear of the absolutely-positioned swap button in the
horizontal sidebar layout.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: mattdawkins

client/src/components/FilterList.vue

@@ -395,6 +395,7 @@ export default defineComponent({
             </template>
             <span>Delete visible items</span>
           </v-tooltip>
+          <v-spacer />
         </v-col>
       </v-row>
     </v-container>