refactor(sidebar): streamline conversation list with completed filter and expand toggle

Replace flat/grouped view toggle with a show-completed filter dropdown,
add expand/collapse-all control, extract status icon component, and
simplify the sidebar header.

src/i18n/messages/pt.json

@@ -834,8 +834,12 @@
       "statsLabel": "{folders} pastas · {convos} conversas",
       "openFolder": "Abrir pasta",
       "searchPlaceholder": "Buscar conversas...",
-      "viewFlat": "Visualização plana",
-      "viewGrouped": "Agrupar por pasta",
+      "showCompleted": "Mostrar conversas concluídas",
+      "moreOptions": "Mais opções",
+      "statusRunningBadge": "Executando",
+      "statusFailedBadge": "Falhou",
+      "conversationCountUnit": "{count, plural, one {# conversa} other {# conversas}}",
+      "emptyFolderHint": "Sem conversas",
       "noMatchingConversations": "Nenhuma conversa correspondente",
       "removeFolderConfirmTitle": "Remover pasta do espaço de trabalho?",
       "removeFolderConfirmDescription": "Remover \"{name}\" do espaço de trabalho? As abas e terminais relacionados serão fechados.",