fix: collapse sidebar by default on small screens

docs/TASKS/app-shell/001-responsive-sidebar-default.md

@@ -0,0 +1,17 @@
+# Responsive Sidebar Default
+
+## Goal
+
+Collapse the authenticated app sidebar by default on smaller devices while preserving the existing desktop expanded default and manual toggle behavior.
+
+## Relevant Files
+
+- `frontend/src/App.vue`
+- `frontend/src/layouts/main/AppSidebar.vue`
+
+## Validation
+
+```bash
+cd frontend
+npm run build
+```