feat(sidebar): add per-page hide toggle with more options dropdown

- Add ``` button in sidebar header with dropdown menu
- Add "Hide sidebar on this page" option with per-page localStorage state
- Show edge indicator (14px chevron) on left when hidden per-page
- Show brief toast notification when hiding
- Fix container margin not resetting when sidebar is per-page hidden
- Add i18n translations for all 10 locales

locales/es.json

@@ -953,9 +953,13 @@
     },
     "sidebar": {
         "modelRoot": "Raíz",
+        "moreOptions": "Más opciones",
         "collapseAll": "Colapsar todas las carpetas",
         "pinSidebar": "Fijar barra lateral",
         "unpinSidebar": "Desfijar barra lateral",
+        "hideOnThisPage": "Ocultar barra lateral en esta página",
+        "showSidebar": "Mostrar barra lateral",
+        "sidebarHiddenNotification": "Barra lateral oculta en la página {page}",
         "switchToListView": "Cambiar a vista de lista",
         "switchToTreeView": "Cambiar a vista de árbol",
         "recursiveOn": "Incluir subcarpetas",