feat(admin): responsive entity nav and collapsible list panels (Phase 9)

EntityNav: hidden on mobile, 48px icon strip at tablet (md), full labels+counts at desktop (lg).
Each list panel collapses to a 32px handle via localStorage-persisted state; auto-collapses when
navigating to the "+New" route. Mobile routing hides the list panel when a detail route is active.

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

frontend/messages/de.json

@@ -161,6 +161,8 @@
 	"admin_tag_edit_heading": "Schlagwort: {name}",
 	"admin_tag_updated": "Schlagwort umbenannt.",
 	"admin_unsaved_warning": "Du hast ungespeicherte Änderungen – speichere oder verwerfe, bevor du wechselst.",
+	"admin_btn_collapse_list": "Liste einklappen",
+	"admin_btn_expand_list": "Liste ausklappen",
 	"admin_btn_edit_tag_label": "Schlagwort bearbeiten",
 	"admin_tag_delete_confirm": "Wirklich löschen? Das Schlagwort wird aus allen Dokumenten entfernt.",
 	"admin_btn_delete_tag_label": "Schlagwort löschen",

frontend/messages/en.json

@@ -161,6 +161,8 @@
 	"admin_tag_edit_heading": "Tag: {name}",
 	"admin_tag_updated": "Tag renamed.",
 	"admin_unsaved_warning": "You have unsaved changes — save or discard before switching.",
+	"admin_btn_collapse_list": "Collapse list",
+	"admin_btn_expand_list": "Expand list",
 	"admin_btn_edit_tag_label": "Edit tag",
 	"admin_tag_delete_confirm": "Really delete? The tag will be removed from all documents.",
 	"admin_btn_delete_tag_label": "Delete tag",

frontend/messages/es.json

@@ -161,6 +161,8 @@
 	"admin_tag_edit_heading": "Etiqueta: {name}",
 	"admin_tag_updated": "Etiqueta renombrada.",
 	"admin_unsaved_warning": "Tienes cambios sin guardar — guarda o descarta antes de cambiar.",
+	"admin_btn_collapse_list": "Contraer lista",
+	"admin_btn_expand_list": "Expandir lista",
 	"admin_btn_edit_tag_label": "Editar etiqueta",
 	"admin_tag_delete_confirm": "¿Realmente eliminar? La etiqueta se eliminará de todos los documentos.",
 	"admin_btn_delete_tag_label": "Eliminar etiqueta",