feat(lists): drag tasks and list entries onto another list; remember open list and view; live pill in lists

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

frontend/src/lib/api.ts

@@ -994,6 +994,13 @@ export const api = {
     await request(`/api/v1/lists/${listId}/items/${itemId}`, { method: 'DELETE' });
   },
 
+  async moveListItem(listId: string, itemId: string, targetListId: string): Promise<ListItem> {
+    return request<ListItem>(`/api/v1/lists/${listId}/items/${itemId}/move`, {
+      method: 'POST',
+      body: JSON.stringify({ targetListId }),
+    });
+  },
+
   async clearCompletedItems(listId: string): Promise<{ removed: number }> {
     return request<{ removed: number }>(`/api/v1/lists/${listId}/clear-completed`, {
       method: 'POST',