fix : reset sidebar state on logout

Add resetSidebar() to useSidebar composable and call it on logout
to prevent stale sidebar data after re-login.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/shared/composables/useSidebar.ts

@@ -29,11 +29,18 @@ export function useSidebar() {
         )
     }
 
+    function resetSidebar() {
+        sections.value = []
+        disabledRoutes.value = []
+        loaded.value = false
+    }
+
     return {
         sections,
         disabledRoutes,
         loaded,
         loadSidebar,
+        resetSidebar,
         isRouteDisabled,
     }
 }